Chapter 3 Fishes - IUCN

Chapter 3. 

The status and distribution 

of freshwater fi shes 

Snoeks, J.¹, Harrison, I.J.² and 

Stiassny, M.L.J.³ 

1 Zoology Department, Royal Museum for Central Africa, Leuvensesteenweg 13, B-3080 Tervuren, Belgium 

and Laboratory of Animal Diversity and Systematics, Katholieke Universiteit Leuven, Charles Deberiotstraat 

32 B-3000 Leuven, Belgium 

2 Conservation International, 2011 Crystal Drive, Suite 500, Arlington, VA 22202, USA 

3 Department of Ichthyology, American Museum of Natural History, Central Park West at 79th Street, New York, 

NY 10024, USA

3.1 Overview of the ichthyofauna of Africa 44 

3.1.1 A short introduction to the ichthyofaunal 

regions 44 

3.2 Conservation status 49 

3.3 Patterns of overall species richness 49 

3.3.1 All fi sh species 49 

3.3.2 Threatened species 55 

3.3.3 Restricted Range species 60 

3.3.4 Data Defi cient species 63 

3.3.5 Extinct species 65 

3.4 Major threats to species 66 

3.5 Research actions required 70 

3.6 Conservation recommendations 71 

Species in the spotlight – The Congo blind barb: 

Mbanza Ngungu’s albino cave fi sh 74 

Species in the spotlight – Tilapia in eastern Africa 

– a friend and foe 76 

Species in the spotlight – Forest remnants in western 

Africa – vanishing islands of sylvan fi shes 79 

Species in the spotlight – A unique species fl ock 

in Lake Tana – the Labeobarbus complex 82 

Species in the spotlight – The Twee River redfi n – 

a Critically Endangered minnow from South Africa 85 

Species in the spotlight – Cauldrons for fi sh 

biodiversity: western Africa’s crater lakes 87

CHAPTER 3 | FISH 

44 

3.1 Overview of the ichthyofauna of 

Africa 

Africa harbours a well-diversifi ed fi sh fauna, resulting from a 

long history of complex climatic and geological events that 

resulted in geographic isolation followed by speciation for 

some populations, or extinction for others (Roberts 1975; 

Lévêque 1997). While the African ichthyofauna shows many 

unique features compared to other continents, it shares 

affi nities with both South America and Asia, as a result of its 

connection to these landmasses as part of Gondwana. 

Africa has several archaic and phylogenetically isolated taxa 

(e.g., the bichirs, Polypteridae; lungfi shes, Protopteridae) 

(Lundberg et al. 2000). Lungfi shes, which include four 

African species in the genus Protopterus, are members of 

the most ancient group of bony fi shes that still have living 

representatives. Fossil lungfi shes date back some 410 million 

years (Le Cointre and Le Guyader 2001), although members 

of the extant genera are younger, originating in the Eocene, 

35-54 million years ago. Africa also has representative 

species groups that have undergone extensive recent 

adaptive radiation, if not even ‘explosive speciation’. The 

best-known case is the 500 or more species of cichlids 

(Cichlidae) in Lake Victoria that went through a major 

lineage diversifi cation about 100,000 years ago (Verheyen 

et al. 2003). While it is clear that the desiccation of Lake 

Victoria about 14,700 years ago had a large infl uence on this 

fauna, the evolutionary impact of a possibly completely dry 

Lake Victoria has been heavily debated (Stager et al. 2004; 

Verheyen et al. 2004). Lundberg et al. (2000) also provide 

other examples, such as the species fl ock of Labeobarbus in 

Lake Tana (see also Species in the spotlight – A unique 

species fl ock in Lake Tana – the Labeobarbus complex) 

and the diversity of sympatric mormyrids found in small 

rivers of the rainforests of western and central Africa. The 

levels of endemism are high for many parts of Africa, with 

some notable examples in the East African Great Lakes, the 

crater lakes (see Species in the Spotlight– Cauldrons 

for fi sh biodiversity: western Africa’s crater lakes) and 

the rivers of central Africa. 

The scientifi c study of African fresh and brackish water fi shes 

is more than a century old. A fi rst major step in compiling 

the existing information was set by George Boulenger, a 

Belgian ichthyologist, then working in the Natural History 

Museum in London. His important four volumes Catalogue 

of the African fi shes (Boulenger 1909-1916) provided the 

most authoritative account of 1,425 species. Even now, this 

catalogue is a major source of information for poorly known 

areas and poorly defi ned taxa. In a more recent effort to 

inventory all the fi shes occurring in African continental 

waters, the Check-List of Freshwater Fishes of Africa 

[CLOFFA] (Daget et al. 1984-1991) listed 2,908 species 

(Boden et al. 2004). CLOFFA represented a considerable 

increase in knowledge, and this knowledge has expanded 

further over the last two decades, as a result of several 

Polypterus endlicherii congicus (LC), a subspecies of bichir 

widespread throughout the Congo catchment and Lake 

Tanganyika. Bichirs are within the Polypteridae family, an archaic 

and phylogenetically isolated group of fi shes. © ULI SCHLIEWEN 

regional accounts. Lévêque et al. (1990, 1992) and Paugy 

et al. (2003a,b) published accounts for western Africa; 

Skelton (1993) published for southern Africa; and Stiassny 

et al. (2007a,b) published for the Lower Guinean region (see 

below). Many of these and other studies, as well as data from 

museum collections from around the world, are synthesized 

in FishBase (Froese and Pauly, 2010), highlighting that the 

total number of scientifi cally known African freshwater 

fi shes has risen dramatically since CLOFFA was compiled. 

For example, currently in FishBase, the number of fi shes in 

the Ethiopian or Afrotropical Zoological realm (that is, Africa 

excluding northern Africa, but including Madagascar and 

the southern part of the Arabian Peninsula) is about 3,200, 

almost all of them endemic to the realm. This endemism is 

not restricted to the species level; the majority of genera are 

endemic, as are about half of the families. In addition, it is 

likely that several hundred species are still to be described 

from the African continent, especially from the Great Lakes 

region, and the Congolian and Angolan river systems. 

3.1.1 A short introduction to the ichthyofaunal regions 

Attempts to subdivide Africa into ichthyofaunal provinces 

dates back more than a century. However, the basis for 

a modern synthesis was formulated by Roberts (1975), 

who based his work on Boulenger (1905); Pellegrin (1911, 

1921, 1933); Nichols, (1928); Blanc (1954); Poll (1957, 

1974); and Matthes (1964). Roberts (1975) recognised ten 

ichthyofaunal provinces (Figure 3.1): 

● Maghreb 

● Abyssinian (Ethiopian) Highlands 

● Nilo-Sudan 

● Upper Guinea 

● Lower Guinea 

● Zaire (Congo) (including lakes Kivu and Tanganyika) 

● East Coast 

● Zambezi 

● Quanza 

● Southern (including Cape of Good Hope) 

The Maghreb province in the north of Africa is quite distinct 

from other regions of continental Africa. It is relatively 

poor in species numbers, with dominance of Cyprinidae 

(Doadrio 1994). In biogeographic terms, this part of the 

continent has a closer affi nity with the Mediterranean part 

of the Palaearctic realm than with the remaining part of 

Africa (Balian et al. 2008b; Lévêque et al. 2008).

Figure 3.1. The major ichthyofaunal provinces of continental Africa, modifi ed from Stiassny et al. (2007a). (1) 

Maghreb, (2) Nilo-Sudan, (3) Abyssinian Highlands, (4) Upper Guinea, (5) Lower Guinea, (6) Congo (Zaire), (7) 

Quanza, (8) Zambezi, (9) East Coast, (10) Southern (including Cape of Good Hope). 

The Nilo-Sudan province is the largest, spanning the total 

width of the continent from Senegal to Mozambique. It 

includes two major river systems, the Nile (but excluding 

lakes Victoria and Edward and their affl uents) and the Niger, 

many West African coastal basins, and the endorheic Lake 

Chad system. It excludes a region spanning the coastal 

basins of the so-called Guinean ridge, from Guinea to 

the western part of Ivory Coast. This is the Upper Guinea 

province (see below), for which the exact boundaries are 

not well defi ned (Lévêque 1997). In a recent review of the 

fi shes of western Africa (Paugy et al. 2003a,b), including 

the Upper Guinea and the Nilo-Sudan provinces, but 

excluding the Nile system, 584 fresh and brackish water 

species were listed. A review of the Nile Basin fauna is long 

overdue, but counts of the River Nile (excluding the region 

of Lakes Victoria and Edward) include 128 species (Witte 

et al. 2009). However, several additional species that are 

endemic to Lakes Tana (Labeobarbus; see Species 

in the spotlight– A unique species fl ock in Lake Tana 

– the Labeobarbus complex), Albert and Turkana 

(haplochromines) should be added to this fi gure. The 

existing inventory of the Nile system is far from complete, 

especially in the poorly documented Sudanese part. In 

addition, the endemic cichlid fauna of Lake Albert contains 

many species that are still to be described (Snoeks pers. 

obs.). 

The Cross River forms the border of the Nilo-Sudan and 

the Lower Guinea province. While the river is considered 

to be part of the Lower Guinea province, its fauna includes 

elements of both provinces (Stiassny and Hopkins 2007). 

The Lower Guinea province included 577 fresh and brackish 

water species at the time of a recent review of its ichthyofauna 

(Stiassny et al. 2007a,b), more than half of which are endemic. 

The region spans the area from the Cross River southwards 

to just north of the Congo Basin. The Shiloango (Chiloango), 

with its lower reaches in Cabinda (Angola), is regarded as 

the southernmost large basin of this area. However, some 

smaller coastal basins with probably a mixed fauna occur in 

the region between the Shiloango and the Congo. 

CHAPTER 3 | FISH 45


46 

A freshly caught specimen of the catfi sh (Euchilichthys 

royauxi) (LC) that lives in large rapids in the Congo River 

basin. © JOHN FRIEL 

The Congo Basin has the largest catchment area of any 

basin in Africa and globally is second only to the Amazon 

(Revenga and Kura 2003). As currently estimated, its 

fi sh fauna includes around 1,250 species. In the east it 

includes part of the Rift Valley region, including lakes Kivu 

and Tanganyika and the Malagarasi system. However, in 

ichthyofaunal terms, Lake Kivu belongs to the East Coast 

province (Snoeks et al. 1997). Lake Tanganyika is a quite 

distinct and noteworthy section of the Congo Basin. It is the 

oldest large lake in Africa which is refl ected in its distinctive 

ichthyofauna. More than 95% of its approximately 200 

cichlids are endemic to the lake, as are more than 60% of 

its non-cichlid species (Snoeks 2000; De Vos et al. 2001). 

Its major affl uent, the Malagarasi contains an ichthyofauna 

of mixed origin (De Vos et al. 2001). Even when disregarding 

the Lake Tanganyika endemics, an estimated 75% of the 

Congo species are endemic. 

The Quanza province is relatively small, including most 

of the coastal basins in Angola, south of the Congo and 

north of the Cunene. An estimate of the number of species 

is diffi cult to give, as this region is one of the least wellknown 

ichthyofaunal provinces in Africa. Poll (1967) listed 

109 freshwater fi sh species from this region, including 

several endemics. 

The Cunene, the Okavango Basin, the large Zambezi 

system and the Limpopo are the major components of 

the Zambezi ichthyofaunal province. On the eastern part, 

the southern border is delimitated by the St. Lucia Basin 

(Skelton 1994). Geographically, Lake Malawi is also part of 

this system. However, the lake’s basin and the Upper Shire 

The confl uence of the Inkisi River and the lower section of the Congo River, D. R. Congo. Only the Amazon and perhaps the 

Mekong have greater fi sh species richness. © ROBERT SCHELLY

The Chobe River, a major tributary of the Zambezi. The 

Zambezi ichthyofaunal province is relatively well known and 

contains many typical sub-Saharan African fi sh families. 

© TRACY FARRELL 

harbour a unique fauna dominated by some 800 or more 

endemic cichlids (Snoeks, 2004), and probably many more 

undescribed species (see section 3.3.1). The remaining 

part of the Zambezi province is relatively well known, 

with species numbers in this region characteristically 

decreasing from north to south (Skelton 2001). 

While the Zambezi province includes many of the typically 

sub-Saharan African fi sh families, this is less evidently the 

case for the southern or Cape ichthyofaunal province, which 

is relatively depauperate in families but high in species 

endemism. The border between the Cape and Zambezi 

provinces is not well defi ned. The Cape province includes 

the Orange system and all basins south of it. However, 

the Orange also includes typical Zambezi elements. Fortytwo 

species occur in the well-known Cape province, 36 of 

which are endemic (Skelton 2001). 

The East Coast ichthyofaunal province is situated to 

the north of the Zambezi province and is relatively poor 

in species and dominated by savanna. Skelton (1994) 

recorded 125 species from the various river systems, with 

an endemicity of about 60%. These systems include all 

coastal basins north of the Zambezi to the Tana system 

in northern Kenya. In this region species richness and 

endemism may well be underestimated, as many of these 

rivers are underexplored. The other main component of 

the province includes a series of lakes of various origins, 

Rukwa, Kivu, Edward, George, Kyoga, Victoria and its 

numerous smaller satellite lakes (Snoeks et al. 1997). All 

these lakes, except Rukwa, have elements of a regional 

super species fl ock, comprising more than 700 endemic 

species of haplochromine cichlids, and many undescribed 

species. 

Roberts’ (1975) work on ichthyofaunal provinces was 

continued by Greenwood (1983) and complemented 

by others (e.g., Skelton 1994; Lévêque 1997; Snoeks 

et al. 1997). While these provinces mostly refl ect past 

and current drainage patterns and are defi ned mainly 

The tigerfi sh, Hydrocynus vittatus (LC), a species popular among the sport fi shing community. This iconic species is generally 

common and abundant with a wide distribution across Africa, but is locally depleted by heavy fi shing pressure. 

© MELANIE L.J. STIASSNY 

CHAPTER 3 | FISH 47


48 

Figure 3.2. A map of the freshwater ecoregions of Africa, from Thieme et al. (2005) 

on a characteristic combination of endemic taxa, their 

boundaries are not always straightforward, and transition 

zones often exist. Thieme et al. (2005) developed a slightly 

different system for defi ning the biogeographic regions of 

Africa, based on ‘freshwater ecoregions’ (See Chapter 1, 

Figure 1.2). 

Thieme et al. (2005) recognised 79 freshwater ecoregions 

on continental Africa (exclusive of Madagascar and 

offshore islands). Abell et al. (2008) subsequently revised 

this, recognising only 78 ecoregions (incorporating the 

Thysville caves into the Lower Congo ecoregion and 

renaming some of the ecoregions) (Figure 3.2). Ecoregions 

were defi ned by a combination of physical and biological 

characteristics, including the hydrological features of 

the region, the communities of aquatic species present, 

and associated ecological and evolutionary processes. 

Consequently, boundaries of ecoregions are not always 

exactly matched to river catchments; in some cases they 

may include partial catchments, or may aggregate subbasins 

that are components of quite different catchments. 

While the ecoregion approach provides very useful 

biological, ecological, and biogeographic information 

about a region, conservation planning and management 

for freshwater ecosystems are usually implemented for 

complete catchments or sub-catchments, rather than 

partial sub-catchments. For these reasons, the method of 

describing species distributions by sub-catchments has 

been adopted by IUCN for the freshwater fi shes included 

in the assessments of the status of freshwater species in 

Africa (e.g., Darwall et al. 2005, 2009; Smith et al. 2009; 

García et al. 2010a; Brooks et al. 2011).

3.2 Conservation status 

Of the 2,836 African freshwater fi sh species assessed 

at the scale of mainland continental Africa (that is, not 

including the four species ranked as ‘Not Applicable’ 

(NA)), over half (57.4% are classifi ed as ‘Least Concern’ 

(see Table 3.1, Figure 3.3). This may be partly explained 

by the large areas of Africa that are sparsely populated 

and where there is relatively little agricultural, industrial, or 

urban development that currently present a severe threat to 

fi shes in other areas (see below). Such undeveloped areas 

include large parts of the Congo Basin, Lower Guinea, 

and regions of southern Africa (Stiassny et al., 2007a,b; 

Tweddle et al. 2009; Stiassny et al., 2011). 

Over 500 species (18% of the classifi ed species) are ‘Data 

Defi cient’ (DD), with insuffi cient information about their 

taxonomy, ecology or distribution to assess whether they 

are threatened or not. This underscores the conclusion 

that a considerable amount of additional surveying and 

monitoring of African freshwaters is required to provide 

a more accurate assessment of the conservation status 

of species in these ecosystems, particularly in parts of 

central Africa and the Rift Valley lakes of eastern Africa 

where numbers of Data Defi cient species are greatest 

(see section 3.3.4 below). Nevertheless, even before such 

surveying and monitoring is implemented, it is possible 

to say that all existing evidence indicates that many 

freshwater fi shes face signifi cant threats. Six hundred 

and nineteen species (with an additional 16 sub-species) 

are classifi ed as threatened – representing 21.8% of all 

assessed species, or 26.6% of all species if one discounts 

the Data Defi cient species. Most of the threatened species 

are in the lowest threatened category, classifi ed as 

‘Vulnerable’ (57.2% of all threatened species), with another 

23.9% of threatened species listed as ‘Endangered,’ and 

18.9% as ‘Critically Endangered’. These fi gures represent 

large numbers of species (Table 3.1), further highlighting 

the severity of threats to African freshwater fi shes. Three 

species are reported as ‘Extinct’, although this is probably 

an underestimate of the true numbers (see section 3.3.5). 

Table 3.1. The number of African freshwater fi sh 

species in each IUCN Red List Category. 

IUCN Red List Category 

Number 

of species 

Number of 

endemic 

species 

Extinct 3 3 

Critically Endangered 117 117 

Endangered 148 148 

Vulnerable 354 353 

Near Threatened 75 73 

Data Defi cient 510 509 

Least Concern 1629 1585 

Total species 2836 2788 

Figure 3.3. The proportion (%) of freshwater fi sh 

species in each regional IUCN Red List Category in 

mainland continental Africa. 

3.3 Patterns of overall species richness 

3.3.1 All fi sh species 

Lévêque (1997) undertook a review of the numbers of 

fresh and brackish water fi shes of Africa according to 

taxonomy (i.e., families, genera, species). Although the 

numbers will have changed since then, his study provides 

a useful overview of taxonomic diversity. He recorded 76 

families in Africa, with the freshwater fauna dominated by 

ostariophysans (1,159 species), many of which are typically 

riverine; however, several families are represented by only 

a few species. The Cyprinidae (475 species) form the 

greatest proportion of ostariophysans, and Characiformes 

are also well represented by the Alestidae (109 species) and 

Distichodontidae (90 species). The Siluriformes (catfi shes) 

include numerous species of Mochokidae (176 species), 

Claroteidae (98 species), and Clariidae (74 species). 

Among the non-ostariophysan groups, Cichlidae is 

the most species rich family, with at least 870 species 

according to Lévêque (1997); most of these are represented 

by species endemic to the lakes of eastern Africa. Other 

families with large numbers of species include the former 

Cyprinodontidae, killifi sh (at least 243 species are currently 

classifi ed in Nothobranchiidae and Poeciliidae), and the 

Mormyridae (elephantfi shes), with 198 species. 

The geographic distribution of species shows some 

distinctive areas of high richness as well as areas of very 

low richness, or even absence of species (Figure 3.4). Not 

surprisingly, in this study there are no fi shes recorded from 

some of the driest parts of Africa, for example, much of the 

Sahara, parts of Ethiopia and Somalia, the Kalahari Desert 

of Botswana, and large parts of Namibia. In contrast, areas 

CHAPTER 3 | FISH 49


50 

Figure 3.4. The distribution of freshwater fi sh species across mainland continental Africa. Species richness = 

number of species per river/lake sub-catchment. 

of greatest species richness include some of the large lakes 

of the Rift Valley of eastern Africa (where cichlids dominate 

the fauna), and the main channel of the Congo River. Of 

the large lakes, Lake Malawi (in the Zambesi ichthyofaunal 

province) has the greatest number of species for which 

assessments have been completed for the IUCN Red List 

(358 species have been assessed). Lake Malawi and its 

infl uents, Lake Malombe and the Upper Shire River that 

connects the two lakes, comprise the Malawi ecoregion 

(Thieme et al. 2005). This region includes an estimated 800 

species of fi shes, most of which are endemic (see section 

3.3.3). However, many are not yet formally described so 

are not assessed for the IUCN Red List. The majority 

of species present are cichlids, mainly represented by 

mouth-brooding haplochromine species. An estimated 67 

of these species (including two introduced species and 

10 that are yet to be formally described) are not cichlids 

(Snoeks 2004). The lake has some economically important 

cyprinids, including a sardine-like pelagic Engraulicypris 

sardella (usipa) (LC), a salmon-like Opsaridium microlepis 

(mpasa), which is Endangered, and a trout-like O. 

microcephalum (sanjika) (VU) (Thieme et al. 2005). Between 

nine and 12 species of mostly deep-water large catfi shes 

of the genus Bathyclarias are endemic to the lake (Snoeks 

2004), appearing to have originated from a widespread 

generalist species, Clarias gariepinus (LCRG), that is also 

present in the lake (Agnese and Teugels 2001). Several 

of the sub-catchments around the lake are also rich in 

species, with a total of 54 non-cichlid species found in the 

affl uent rivers (Snoeks 2004).

Haplochromis desfontainii (EN) is from Algeria and Tunisia, 

where it is found in warm, freshwater springs. It is a member 

of the Cichlidae family, the most speciose in Africa. 

© ANTON LAMBOJ 

The Lake Tanganyika Basin (part of the Congo Basin 

ichthyofaunal province) harbours an estimated 470 species 

of fi shes, 287 of which had been formally described from 

the lake itself at the time these numbers were reported by 

Thieme et al. (2005). The lake has high levels of endemism, 

especially for cichlids (see section 3.3.3). Around 300 of 

the 470 recorded species (64%) are cichlids, including 

species-rich lineages of substrate-brooding as well as 

mouth-brooding cichlids (Coulter 1991; De Vos and 

Lake Malawi ecoregion includes an estimated 800 species 

of fi shes, most of which are endemic and from the family 

Cichlidae. © FRANK DOUWES 

Mormyrops anguilloides (LC), a species of elephant fi sh 

widespread in Sub-Saharan Africa. It is a member of the 

Mormyridae family, one of the most species-rich families in 

Africa. © JOHN FRIEL 

Snoeks 1994; Snoeks 2000; Thieme et al. 2005). Thieme 

et al. (2005) note that the lake also has species fl ocks of 

catfi shes (Claroteidae and Mochokidae), snooks (Latidae) 

and spiny eels (Mastacembelidae). The lake also supports 

a unique community of pelagic fi shes including endemic 

clupeids (Limnothrissa miodon (LC) and Stolothrissa 

tanganicae (LC)) that are prey to several other species 

and which support an off-shore fi shery in the lake (Thieme 

et al. 2005). Affl uent drainages at the northern tip of the 

lake support up to 43 species, while the lower section 

of the Malagarasi on the eastern shore of the lake holds 

the highest number of species (71 species have been 

assessed) for any of the affl uents. 

Estimates for the total number of species in Lake Victoria 

(part of the East Coast province) are variable, although 

Thieme et al. (2005) note there may be more than 600 

endemic species. Most of these are cichlids, and several 

are Critically Endangered or Possibly Extinct (see section 

3.3.2 and 3.3.5). Many of the endemic species of cichlids 

are thought to have gone extinct since the 1980s (Harrison 

and Stiassny 1999). The sub-catchments adjacent to Lake 

Victoria hold between 21 and 51 species that have been 

assessed for the Red List, with the greatest numbers found 

in the Nzoia drainage to the north-east of the lake. 

More than 858 fi sh species have been assessed for the 

Congo Basin (i.e., that part of the Congo ichthyological 

province exclusive of the Rift Valley lakes Tanganyika) 

(Stiassny et al. 2011). This number is certainly an 

underestimate, and many of these regions are poorly 

explored or not explored at all; the recorded number is 

increasing as more species are described each year 

(Stiassny et al. 2011). For example, recent surveys in the 

lower section of the Congo River downstream of Malebo 

CHAPTER 3 | FISH 51


52 

The Malebo Pool, one of the most species-rich areas currently known throughout the Congo catchment. © ROBERT SCHELLY 

Pool have more than doubled the number of species 

documented there, including the identifi cation of more 

than 10 new species in the last fi ve years (Stiassny et al. 

2011). 

The main courses of the major rivers of the Congo Basin 

have particularly high numbers of species, with more 

than 150 species reported for most reaches of the Congo 

River, as well as sections of the Lualaba, Kasai, Ubangi/ 

Uele, and Sangha rivers. The middle section of the 

Congo, between Boyoma Falls and Malebo Pool, has the 

greatest species numbers, with several sections having 

more than 250 assessed species, while the Malebo Pool 

region itself has 316 assessed fi sh species. However, the 

smaller tributaries distributed throughout the Congo Basin 

have fewer species; fewer than 30 in many cases, and 

some sub-catchments had no species recorded in these 

biodiversity assessments. This apparent distribution of 

species is likely an artifact of more intensive sampling that 

has occurred in the larger channels of the Congo Basin 

compared to the smaller, more inaccessible, tributaries. 

Recent surveys of small river basins in the lower Congo 

region such as the Inkisi, Nsele, and Mpozo have, for 

example, found them to harbour many more species than 

previously documented (Thieme et al. 2008; Wamuini et al. 

2008; Monsembula pers. comm.; Schliewen pers. comm.), 

and similar observations are being made throughout 

other parts of the basin as inventories are undertaken. 

An excellent case in point is the Léfi ni River, from which 

virtually no species were known until recently when, after 

a thorough exploration of its lower reaches, it was found to 

harbour 140 species (Ibala-Zamba 2010). 

The equatorial location, large size and the relative longevity 

and climatic stability of the forested, moist tropical regions 

of central Africa contribute to the high levels of species 

This species of freshwater pufferfi sh, Tetraodon miurus (LC), 

captured in the Odzala National Park, D. R. Congo, is quite 

widespread throughout the Lower Congo River basin. 

© JOHN FRIEL

Rapids on the Dja River fl owing to the Congo basin. The Dja 

River headwaters were once captured by rivers of Lower 

Guinea, possibly the reason why the two regions share some 

ichthyological fauna. © TIMO MORITZ 

richness in this area (Kamdem Toham et al. 2006; Thieme 

et al. 2008). In addition, the region has a complex mosaic 

of habitats, contributing to 19 freshwater ecoregions, often 

with distinct hydrographic barriers between the habitats 

(for example, waterfalls and rapids); all of these factors 

appear to promote high species diversifi cation (Thieme 

et al. 2005; Brummett et al. 2009; Markert et al. 2010; 

Stiassny et al. 2010). 

Although the species richness observed in the Congo 

Basin and the east African Rift Valley lakes exceeds that 

observed in any other part of Africa, there are several 

other regions that have a relatively high species richness 

distributed over large areas. This is particularly noticeable 

over almost all of the Lower Guinean ichthyological 

province and large parts of western Africa (covering the 

western part of the Nilo-Sudan, and the Upper Guinea 

ichthyological provinces). 

The Lower Guinea province is adjacent to the Congo 

Basin, and the two regions share some fauna, perhaps as 

a consequence of historic capture of the headwaters of 

Congo Basin rivers by Lower Guinean rivers (for example, 

capture of the Dja headwaters by the Nyong, Ntem, Ivindo) 

(Thys van den Audenaerde 1966; Stiassny et al. 2011). 

More than 550 species have been reported from Lower 

Guinea (Stiassny et al. 2007a,b). The most species-rich 

drainages are the lower part of the Sanaga (Cameroon), 

the Ogowe (Gabon), the upper Ngounie (Gabon/Republic 

of Congo), and the lower Kouilou systems (Republic of 

Congo), each having over 100 recorded (and assessed) 

species. Most sub-catchments of the Lower Guinean 

province have between 50 and 100 assessed species. 

These include several coastal rivers that are relatively short 

(i.e., 60km or less) and are disproportionately rich in fi sh 

species relative to their small size. Lower Guinea has been 

a focus for ichthyological survey over the last 20 years. 

This has promoted extensive taxonomic and revisionary 

work, including the description of many new species and 

Protopterus annectens (LC), the African lungfi sh. Lungfi sh 

are adapted to survive periods of drought by burrowing to 

the bottom of mud in drying pools and aestivating there for 

up to eight months. © TIMO MORITZ 

the production of a guide to the freshwater fi sh fauna of 

the region (Stiassny et al. 2007a,b). 

Similarly, much of western Africa has been well studied, 

especially over the latter part of the 20th century and early 

21st century, with the production of taxonomic revisions 

and faunal guides (e.g., Paugy et al. 2003a,b). It is probably 

one of the better-known large areas after southern Africa. 

Western Africa includes 17 freshwater ecoregions, 

distributed through the western parts of the Nilo-Sudan 

province and the Upper Guinea province. According to 

Paugy et al. (2003a), there are 584 species of fresh and 

brackish water fi shes distributed through western Africa; 

521 of these species (the freshwater component) were 

assessed for the Red List (Laleye and Entsua-Mensah 

2009). 

While several river basins in western Africa have relatively 

high species numbers, the region is less uniformly rich in 

species than the Lower Guinea province of central Africa. 

The Niger River, which fl ows more or less from west to 

east across a large part of western Africa, and is Africa’s 

third longest river, has a patchy species density pattern. 

Those parts of western Africa that are richest in species 

tend to be the coastal basins, moist forests and woodland 

savanna, whereas those that have fewer species are 

found in the Sahel, where conditions are drier and rivers 

are smaller (with the exception of the Niger) or may fl ow 

only seasonally. Fishes found in these drier regions often 

show adaptations to periods of drought. For example, the 

lungfi sh, Protopterus annectens (LC) is an air breather (and 

must take lungfuls of air occasionally in order to survive) 

and can burrow into mud at the bottom of drying pools 

and survive there, aestivating, usually for up to seven or 

eight months; this may be extended experimentally to 

up to four years in P. aethiopicus (Helfmann et al. 1997). 

There are also species of killifi sh (e.g., Pronothobranchius 

kiyawensis (NT)) that have drought resistant eggs (Laleye 

and Entsua-Mensah 2009). 

CHAPTER 3 | FISH 53


54 

The turquoise killifi sh, Nothobranchius furzeri (LC), from the Bahini National Park in Mozambique. This beautiful killifi sh is 

typically found in seasonal pans, which they often share with lungfi shes. They lay drought-resistant eggs, and are apparently 

one of the shortest lived killifi shes (four to fi ve months). © SAIAB/ROGER BILLS 

The greatest numbers of species in western Africa are 

found in the Niger Delta ecoregion (152 species have 

been assessed). The delta and surrounding areas are 

also some of the most heavily impacted areas in Africa 

(see section 3.3.2). To the west, 107 species have been 

assessed in the Ogun River basin in the region of the 

Lagos Lagoon, including six threatened species (see 

section 3.3.2). Several catchments and sub-catchments 

of western Africa have more than 70 species, particularly 

those in the Upper Guinea province (covering parts of 

southern Guinea, Sierra Leone, and Liberia), the Upper 

Niger and Inner Niger Delta ecoregions (in Guinea and 

Mali), and some coastal catchments from Ivory Coast to 

south-western Nigeria. The Volta ecoregion (including 

Lake Volta) has between 160 and 185 species (Laleye and 

Entsua-Mensah 2009). According to recent biodiversity 

assessments, 105 fi sh species are present in the lake 

itself; however, this number may be misleading, since it 

probably includes species found in drainages close to the 

lake in riverine and marginal habitats. Construction of the 

Akosombo and Kpong dams has signifi cantly affected the 

ecology of the region (most noticeably by the formation 

of Lake Volta) and has contributed to the decline of some 

species (Thieme et al. 2005; and see section 3.3.5). 

The northern parts of the Nilo-Sudan province in western 

Africa, which include the middle reaches of the Niger 

River, are situated in the Sahel, where species richness is 

muted (see above). An exception to this is the endorheic 

Lake Chad (with 69 species) and the region covering the 

Yedseram and lower Chari river basins (with 72 species 

recorded), both of which are major affl uents of Lake 

Chad. Many of the species in the region are adapted to 

patterns of seasonal fl ooding in the lake and around the 

lake margins. 

Other parts of Africa have lower species numbers 

compared to western Africa, Lower Guinea, the Congo, 

and the Rift Valley lakes discussed above. While the Nile 

River is the longest in the world (Revenga and Kura 2003), 

fewer than 30 species are recorded and assessed for most 

of its length. Many affl uents of the main channel, in both 

the Upper and Lower Nile ecoregions, and throughout 

much of the Ethiopian Highlands province, have fewer 

than fi ve species recorded. This is probably a refl ection of 

the aridity within much of the Nile’s catchment area, where 

affl uents tend to be small, and many fl ow intermittently 

and are unable to support large numbers of species. 

Nevertheless, part of the reason for low recorded species 

numbers is the limited exploration of large parts of the 

basin within Sudan (covering some of the Lower Nile and 

all of the Upper Nile ecoregions), including the vast Sudd 

swamps in southern Sudan. 

There are some exceptions to the low species numbers 

recorded in the Nile Basin. The greatest numbers of 

species (where 40 to 50 species have been assessed) are 

found upstream from Khartoum in the Blue Nile system, 

and in the wetlands around Gambela National Park (in 

the westernmost part of Ethiopia) that drain to the White 

Nile. Forty seven species from Lake Nasser, formed by the 

Aswan Dam, have been recorded and assessed. Despite 

this elevated number of species, the overall impact of the 

dam has been detrimental to the freshwater fi sh fauna 

of the Nile system (just as with Lake Volta in western 

Africa; see above) (see section 3.3.2), with many species 

apparently extirpated from the former parts of their range 

below the dam. 

Most of the East Coast province just south of the Ethiopian 

Highlands, and the eastern part of the Nilo-Sudan province, 

have low species richness. Lake Victoria and its satellite 

lakes and affl uent rivers (discussed above) are the most 

noteworthy exceptions to this. Twenty nine species are 

recorded and assessed for the Tana River basin in Kenya, 

39 in the Ruvu and Rufi ji river basins in Tanzania, and 25

in the Ruvuma River on the border between Tanzania and 

Mozambique. Otherwise, most of the east coast basins 

have fewer than 20 species, providing a striking contrast 

with the species rich coastal basins of Lower Guinea on 

the other side of the continent, and probably refl ecting a 

combination of limited survey and the well-documented 

episodes of aridity experienced by eastern Africa. 

Southern Africa encompasses the Quanza, Zambezi, and 

Cape ichthyofaunal provinces; it includes 22 freshwater 

ecoregions and some very diverse habitat types. The 

general pattern is one of declining species richness 

towards the west and south. For example, most of the subcatchments 

of South Africa have fewer than 10 species. 

Highest species richness is found in parts of the Zambezi 

basin upstream from Lake Kariba (more than 50 species 

are recorded in many sub-catchments, and 80 species 

are present immediately upriver from the lake itself) and 

in the lowest parts of the basin; in parts of the Okavango 

basin; some higher parts of the Limpopo basin; the Buzi 

and Save basins; the Incomati-Pongola system; and some 

smaller coastal basins in Mozambique. However, some of 

these densities appear, in part, to refl ect the intensity of 

collection efforts (Tweddle et al. 2009). 

3.3.2 Threatened species 

The distribution of threatened freshwater fi sh species 

(Figure 3.5) is largely focused in a band that runs along the 

coast of western Africa and the Lower Guinea province 

from Senegal to D. R. Congo, throughout the Zambezi/ 

Okavango basins in the northern part of southern Africa, 

through the river basins and lakes of the Rift Valley of 

eastern Africa, also including some of the coastal basins 

of eastern Africa, and some basins in the eastern and 

southern parts of South Africa. There are a few pockets of 

threatened species along the Uele River in central Africa, in 

the region of Lake Tana in north-eastern Africa, and in the 

Atlantic and Mediterranean Northwest Africa freshwater 

ecoregions in the Maghreb region of northern Africa 

The absence of threatened species throughout most of 

the arid areas of northern Africa, and parts of the Horn 

of Africa (comprising Somalia and eastern Ethiopia), as 

well some parts of southern Africa (especially Namibia 

and Botswana) is unsurprising; fi shes are totally absent 

from many of these regions (see above). Some other 

sub-catchments may have only a very small number of 

species (e.g., fewer than three species) but in these cases 

The Lugenda River is located in northern Mozambique, where it fl ows from Lake Amaramba and forms the largest tributary of 

the Ruvuma River. The Lugenda River Valley’s rich wildlife has led to development of the area as a destination for ecotourism. 

Within the river itself, species such as Barbus atkinsoni, Labeo cylindricus and Oreochromis placidus, together with around 40 

other species of fi sh, sustain an important local fi shery. © SAIAB/ROGER BILLS 

CHAPTER 3 | FISH 55


56 

Figure 3.5. The distribution of threatened freshwater fi sh species across mainland continental Africa. Species 

richness = number of species per river/lake sub-catchment. 

Aphanius saourensis (CR), the Sahara 

aphanius, is a species of killifi sh 

(Cyprinodontidae family) endemic to 

Algeria. Many killifi sh species survive 

periods of drought by having droughtresistant 

eggs. © HEIKO KAERST

Figure 3.6. The proportion of freshwater fi sh species that are threatened within each sub-catchment across 

mainland continental Africa. Species richness = proportion of species per river/lake sub-catchment that are 

threatened. 

between 44% and 75% of the species are threatened; this 

is the case for some sub-catchments in the Maghreb and 

in the Etosha and the Karstveld Sink Holes ecoregions in 

Namibia (Figure 3.6). 

One Critically Endangered species, the Sahara aphanius 

(Aphanius saourensi), is present in the Sahara freshwater 

ecoregion. This species is endemic to the Oued Saoura 

Basin, but has disappeared from several parts of the 

basin and is now restricted to a single population found 

near Mazzer in the Sahara desert (García et al. 2010b). 

Excessive groundwater extraction for agriculture, pollution 

of remaining wetlands, and introduction and proliferation of 

mosquitofi sh (Gambusia holbrooki) are the main reasons for 

this decline. There are two species of fi shes from northern 

Africa that are considered Endangered. Haplochromis 

desfontainii (EN) and Pseudophoxinus punicus (EN), native 

to Tunisia and Algeria, are threatened by groundwater 

extraction, dams, water pollution and drought, which 

widely affect the area (García et al. 2010b). 

Most of the Nile Basin lacks globally threatened species, 

with the exception of the upper part of the basin (adjacent 

to Lake Victoria), and in the vicinity of Lake Tana. High 

proportions of threatened species (44% to 75% of the 

species assessed) are found in Lake Victoria and several 

of the adjoining sub-catchments. Between 26% and 43% 

of assessed species are threatened in the region of Lake 

CHAPTER 3 | FISH 57


58 

A Lake Malawi cichlid from the group of rock-dwelling 

species collectively known as ‘mbuna’. These species are 

endemic to the lake, and many have extremely restricted 

ranges. © SARAH DEPPER 

Tana, with seven threatened species in Lake Tana itself 

(see Species in the spotlight– A unique species fl ock 

in Lake Tana – the Labeobarbus complex). Although 

globally threatened species are not recorded throughout 

the rest of the Nile Basin, it is important to note that several 

species in the basin have undergone serious declines 

in the northern African parts of their range. García et al. 

(2010b) note that at least 80% of the 24 northern African 

freshwater fi shes listed as Regionally Extinct (to northern 

Africa) were previously found in the Nile Basin in Egypt, 

and the construction of the Aswan Dam was a major cause 

of these extirpations. 

The low numbers of threatened species recorded for much 

of central Africa, including the species rich Congo Basin, 

may be partly attributed to the lack of human development 

in many parts of this region. However, several parts of 

central Africa are also insuffi ciently surveyed to accurately 

assess threats to species found there (see section 3.3.4 

on Data Defi cient species). Moreover, in some tributaries 

of the Sangha River, and tributaries of the Kwango River 

draining to the Kasai, the ratio of threatened species to the 

total species richness is still relatively high (26% or more). 

The highest number of threatened species occurs in 

Lake Malawi, where there are 105 recorded threatened 

species (28% of the total species assessed for this lake). 

A number of these assessments are, however, based on 

the ecological characteristics of many cichlid species, 

such as their highly restricted ranges and low numbers 

of offspring, which make them particularly vulnerable to 

extinction. Given the more recent requirement to also 

document evidence of current or imminent threats to a 

species for it to be assessed as threatened, it is possible 

some may be downgraded to a lower Red List category 

when next re-assessed. The rock-dwelling cichlids, often 

called mbuna, have particularly restricted distributions 

(intra-lacustrine endemism). These cichlids grow slowly 

and produce small numbers of offspring, are extremely 

vulnerable to habitat degradation and exploitation, and 

recover slowly from population declines (Ribbink 2001; 

Thieme et al. 2005). The potamodromous species that 

migrate from the lake into affl uent rivers to spawn are 

also threatened by fi sheries operations at the river mouths 

where they congregate during migration, and by degraded 

spawning habitats within the rivers (Tweddle 1996). 

Lake Victoria has the next highest number of threatened 

species (81 species; 44% of the assessed species in the 

lake), resulting from a combination of well-documented 

threats, including: the introduction of the piscivorous 

predator, Nile perch (Lates niloticus), and the water 

hyacinth (Eichornia crassipes) which has reduced light and 

oxygen levels in the lake’s waters; overfi shing and use of 

fi sh poisons; and habitat deterioration and eutrophication 

resulting from increasing lakeside agriculture, urbanisation, 

and deforestation (for further discussion and extensive 

references see Harrison and Stiassny 1999; Kaufman 

1992; Witte et al. 1992a,b; Kaufman and Ochumba 

1993; Seehausen and Witte 1995; Oijen and Witte 1996; 

Seehausen 1996; Seehausen et al. 1997a,b; Kaufman 

et al. 1997; Witte et al., 2007) (also see Chapter 1, Box 

1). Witte et al (1992b) initially estimated that as many as 

200 species of haplochromine cichlid in Lake Victoria had 

disappeared or were threatened with extinction within the 

lake. Harrison and Stiassny (1999) recognised that the lake 

was undergoing catastrophic ecological and limnological 

changes that represent a serious threat to the endemic 

cichlids; nevertheless, they believed it was premature to 

suggest that many of these species were actually extinct, 

because Witte et al (1992b) were using data limited to an 

11-year period for a small part of the lake (Mwanza Gulf), 

which could not be extrapolated to the whole lake and used 

as a measure of extinction. Harrison and Stiassny (1999: 

table 9) listed 48 species of cichlids from Lake Victoria 

that might be extinct but could not be confi rmed as such 

because of complications in their taxonomy (in most cases, 

the species had not been scientifi cally described). They 

listed another 54 species (Harrison and Stiassny 1999: 

table 10) that might be extinct but could not be confi rmed 

as such because of inadequate surveying and sampling, 

and 30 species (Harrison and Stiassny 1999: table 11), 

which could not be classifi ed as probably or possibly 

extinct, due to a lack of data. Harrison and Stiassny’s 

caution in classifying the Lake Victoria cichlids as extinct 

has been supported by evidence of a resurgence in several 

of the species, with greater resurgence of zooplanktivores 

compared to detritivores (Witte et al. 2007). Even with this 

resurgence, the threats to many of the species in Lake 

Victoria are still quite evident, and it is pragmatic to record

them in categories of high threat (52 species are Critically 

Endangered, and many of these are also noted in IUCN’s 

database as Possibly Extinct). Nevertheless, many fi sh 

species in the lake remain Data Defi cient (see section 3.3.4), 

and more extensive surveying and sampling are required 

throughout Lake Victoria to fully assess the conservation 

status of the cichlid species present. Because Lake Victoria 

is Africa’s largest lake by area, this represents a signifi cant 

challenge. Moreover, there would be the requirement for a 

larger number of highly trained taxonomists than currently 

exist in Africa, or elsewhere, to identify the 600 or more of 

species amongst the many thousands of specimens that 

would be collected. In light of this taxonomic impediment, 

an ecological classifi cation of Lake Victoria’s cichlids into 

trophic guilds may offer a pragmatic, short-term solution 

(Witte et al. 2007). 

There are 12 threatened species in Lake Tanganyika (5% 

of the total number of 245 species recorded in the Red List 

assessments). The overall number of threatened species 

is lower than in Lake Malawi partly because there are 

fewer species present in Lake Tanganyika; the proportion 

of threatened species (relative to the total number) is lower 

compared to Lakes Victoria and Malawi because the threats 

are generally more localized (Cohen et al. 1995) (especially 

compared to Lake Victoria); and the Tanganyikan species 

tend to have a wider distribution, extending into areas 

where there are fewer threats. 

Outside the area of the large lakes of the African Rift 

Valley, the regions with high numbers of threatened 

species occur in and around the rapids in the Lower 

Congo and some coastal basins in western Africa and 

Lower Guinea. The Lower Congo has up to 24 threatened 

species just upstream of Inga, and has one Critically 

Endangered species of cichlid, Teleogramma brichardi, 

apparently restricted to the Kinsuka rapids near Kinshasa. 

This species is increasingly threatened by the impacts 

of urbanization at Kinshasa and Brazzaville (Stiassny et 

al. 2011). However, further collections are necessary to 

establish the precise distribution of this species. Several 

other Endangered species are found, especially in the 

vicinity of Malebo Pool. 

At least 13 threatened species are found in the delta region 

of the Niger River, including two Critically Endangered 

species that are threatened by the impacts oil exploration 

in the delta, the distichodontid Neolebias powelli and the 

killifi sh Fundulopanchax powelli. Six threatened species 

are recorded nearby, in the species rich lower Ogun River 

at Lagos lagoon. These species are threatened mainly 

by deforestation (e.g., Brycinus brevis, assessed as 

Vulnerable), as well as agricultural and urban development 

(e.g., the mormyrid Marcusenius brucii, assessed as 

Vulnerable); however, the small red-eyed tetra, an alestid, 

Arnoldichthys spilopterus (assessed as Vulnerable) is 

threatened by an extensive harvesting for the aquarium 

Teleogramma brichardi (CR), from Kinsuka rapids near 

Kinshasa, D. R. Congo. © MELANIE L.J. STIASSNY 

fi sh trade. Just north of the Niger Delta, in a tributary of 

the Benue River on the Bauchi plateau, the cyprinid Garra 

trewavasae is Critically Endangered due to the impacts of 

tin mining. 

At least 10 threatened species are found in the coastal 

drainages of Sierra Leone and Liberia; these include some 

Critically Endangered species (e.g., Labeo currie, Barbus 

carcharinoides, Epiplatys ruhkopfi , Tilapia cessiana and T. 

coffea), and several Endangered species, especially in the 

vicinity of the St. Paul and Lofa rivers. These species are 

threatened by habitat degradation caused by deforestation 

and mining. In the Konkouré River in Guinea, the catfi sh 

Synodontis dekimpei is Critically Endangered for the same 

reasons. In the Fouta-Djalon ecoregion of Guinea, the 

killifi sh Scriptaphyosemion cauveti, a Critically Endangered 

species from a tributary to the Kolenté River, is threatened 

by expansion of the nearby city of Kindia. 

Twenty six threatened species are recorded from the 

Western Equatorial Crater Lakes freshwater ecoregion 

and the river drainages nearby, at the border of south-west 

Cameroon and Nigeria (see Species in the spotlight – 

Cauldrons for fi sh biodiversity: western Africa’s crater 

lakes). Many of these species are Endangered or Critically 

Endangered, and the majority are cichlids endemic to 

crater lakes, although there are also several killifi shes, 

Neolebias powelli (CR), a small riverine pelagic distichodontid 

characiform, is endemic to a very localised part of the Lower 

Niger Delta, where it is threatened by oil exploration within 

the delta. © TIMO MORITIZ 

CHAPTER 3 | FISH 59


60 

Denticeps clupeoides (VU), from the Iguidi River, south-east 

Benin (see Species in the Spotlight: Forest remnants in 

western Africa – vanishing islands of sylvan fi shes). 

© TIMO MORITZ 

and some cyprinids and catfi shes. Within Lower Guinea, 

high numbers of threatened species (12 to 14 species) are 

found in sections of the Ivindo, Bouniandjé and Nouna (a 

tributary to the upper Ivindo) systems. 

In eastern and southern Africa, the number of threatened 

species is low for most basins (excluding the Rift Valley 

lakes). The greatest numbers in eastern Africa are found in 

the small Ruvu River, a coastal basin near Dar es Salaam 

that harbours nine threatened species. Although other 

basins in eastern Africa have fewer numbers of threatened 

species, some include one or more Critically Endangered 

species, which in most cases are are cichlids. For example, 

Oreochromis pangani, is a Critically Endangered species 

from the Pangani basin, which has been impacted by 

several different threats. Outbreaks of disease reduced the 

population in the late 1960s; subsequently, overfi shing and 

fi shing with illegal gear, as well as siltation and pollution, 

have continued to threaten populations. The clearance of 

macrophytes also removed important refuges and feeding 

areas for the fi sh. Orthochromis uvinzae is restricted to the 

middle Malagarasi River drainage to Lake Tanganyika, in 

Tanzania, and is impacted by habitat loss. Oreochromis 

chungruensis is endemic to Lake Chungruru, a crater lake 

north of Lake Malawi, and is impacted by siltation and 

dropping water level. 

In southern Africa, the Olifants River in the southwest 

part of South Africa has the greatest numbers of 

threatened species, with seven species (70% to 75% of 

all assessed species in the Olifants basin), including two 

Critically Endangered species, Barbus erubescens (see 

Species in the spotlight– The Twee River redfi n – 

a Critically Endangered minnow from South Africa) 

and an undescribed species of Pseudobarbus. Both 

are threatened by competition with, and predation by, 

introduced species, as well as deterioration in habitat and 

water abstraction caused by intensive farming. Slightly to 

the south, in the Tradou catchment of the Breede River 

system, Pseudobarbus burchelli is similarly Critically 

Endangered due to introduced species and pollution. A 

number of other species are also assessed as Endangered 

in the southern part of South Africa and in Lesotho (e.g., 

Pseudobarbus asper and the Maloti minnow, Pseudobarbus 

quathlambae), where they face similar threats to the abovementioned 

species. Tweddle et al. (2009) gives a short 

account of the Maloti minnow conservation project. South 

Africa and Mozambique also harbour some undescribed 

but Critically Endangered species of Pseudobarbus, 

Kneria and Barbus. Two Critically Endangered species 

are found in the Karstveld Sinkholes ecoregion of central 

Namibia: one is Tilapia guinasana, which occurs naturally 

only in Lake Guinas. where it is threatened by groundwater 

extraction, as well as competition and predation from, as 

well as possible hybridization with, introduced tilapiines; 

and the other is the cave catfi sh, Clarias cavernicola, 

known only from a single tiny lake (18m by 2.5m) in the 

Aigamas Cave, near the town of Otavi, which is threatened 

by over abstraction of water and might also be impacted 

by collections made for the aquarist trade. 

There are three Critically Endangered species in the Zambezi 

River basin. An undescribed species of Barbus (Barbus sp. nov. 

Banhine) is known from four neighbouring sites at the southeastern 

edge of the Banhine National Park in Mozambique, 

in the Zambezian Lowveld freshwater ecoregion. In the upper 

Zambezi fl oodplain ecoregion, Neolebias lozii is restricted 

to the Sianda River that has been canalised, probably to 

aid drainage for agriculture. Unlike most other Critically 

Endangered species with restricted distributions, the cichlid 

Oreochromis mortimeri is widely distributed in the Middle 

Zambezi-Luangwa ecoregion and parts of the Zambezian 

Highveld ecoregion. This species is threatened mainly by the 

widespread introduction of O. niloticus, which is displacing it 

throughout much of its range. 

3.3.3 Restricted Range species 

Restricted range species (identifi ed as those species with 

distribution ranges of less than 50,000km²) are found in 

several African sub-catchments, but mainly in Upper and 

Lower Guinea, and some parts of the Congo Basin, and 

in eastern and southern Africa (particularly in the Cape 

Province of South Africa) (Figure 3.7). Most sub-catchments 

have only one to three restricted range species recorded 

(although this is likely to be an underestimate in some 

areas; see below). The largest of the Rift Valley lakes have 

many more restricted range species than are found in any 

other part of the continent. The high numbers of restricted 

range species found in the Rift Valley lakes are largely 

due to the endemic species-rich fl ocks of cichlids found 

in these lakes. For example, 99% of cichlid species in 

Lake Malawi are endemic, and more than 95% of the Lake 

Tanganyika cichlids are endemic (Snoeks 2000). Lake Kivu, 

to the north of Lake Tanganyika, harbours 15 restricted 

range species, while the Western Equatorial Crater Lakes 

ecoregion in Cameroon harbours 12. The restricted range

Figure 3.7. The distribution of restricted range freshwater fi sh species across mainland continental Africa. 

Species richness = number of species per river/lake sub-catchment. 

species in the crater lakes are also mainly cichlids. Many 

of those lakes with restricted range species, which also 

hold Critically Endangered and Endangered species, are 

potential candidates for designation as Key Biodiversity 

Areas, or possibly Alliance for Zero Extinction sites (see 

chapter 8, section 8.3). 

Lake Turkana, to the north-east of Lake Victoria, has nine 

restricted range species. Unlike the other large lakes of 

the Rift Valley, the fi sh fauna of Lake Turkana is composed 

mainly of nilotic riverine species rather than cichlids. Lake 

Tana in Ethiopia has eight restricted range species, mostly 

represented by the species fl ock of endemic cyprinids of 

the genus Labeobarbus (see Species in the spotlight – 

A unique species fl ock in Lake Tana – the Labeobarbus 

complex). 

Lake Tanganyika 

contains many 

restricted range 

cichlid species, 

95% of which are 

endemic to the 

lake. © JOHN FRIEL 

CHAPTER 3 | FISH 61


62 

A selection of the rocky shore cichlid species endemic to Lake Tanganyika. © SASKIA MARIJNISSEN 

A number of rivers also have notably higher numbers of 

restricted range species. In the Upper Guinea province, 

the relatively small coastal basins of the Lofa, St. Paul, St. 

John, and Cess rivers have between fi ve and 12 restricted 

range species, the greatest number being in the Cess. 

Up to 17 restricted range species are found in the vicinity 

of Inga, in the lower part of the Lower Congo Rapids 

ecoregion. These species, some of which are assessed as 

Endangered, most likely show restricted ranges because 

they are adapted to the fast currents, low light intensity, 

The largemouth yellowfi sh, Labeobarbus kimberleyensis (NT), 

is endemic to the Orange River system in South Africa, where 

it is reasonably common, especially in large deeper pools in 

the middle and lower Vaal and Orange rivers, respectively. It 

is promoted as a fl agship angling species, with most anglers 

practising catch and release. © SAIAB/ROGER BILLS 

and high turbidity of the rapids. They are also likely to 

be impacted by development of the hydropower dam 

complex at Inga (see section 3.3.2). The current state of 

knowledge of the taxonomy and biogeography of species 

in the Lower Congo is incomplete, but recent research has 

identifi ed many more species than were previously known 

(Lowenstein et al. 2011; Stiassny et al. 2011). It is probable 

that more restricted range species will be found in the 

Lower Congo rapids region as surveys there continue. 

The Upper Congo rapids ecoregion also has marginally 

higher numbers of restricted range species (seven species) 

compared to surrounding areas, probably for the same 

reason as for the Lower Congo rapids (see above). Other 

parts of the Congo Basin with high numbers of restricted 

range species include the Ubangi River in the region of Bangui 

(six species), the Lubi basin draining to the Sankuru (seven 

species), the upper part of the Lowa Basin near Lake Kivu, 

and in several parts of the Lufi ra, Luvira, and Luapula basins 

in the Upper Lualaba and Bangweulu-Mweru ecoregions 

(all with fi ve restricted range species). In the Lower Guinea 

province, the greatest numbers of restricted range species 

(fi ve to eight species) are found in the Ivindo and upper parts 

of the Ogowe, and in the lower Sanaga River. 

The rivers of eastern and southern Africa have fewer 

restricted range species, possibly a consequence of the 

generally lower numbers of species found there. The 

sub-catchments with the greatest numbers of restricted 

range species are: the upper part of the Tana River, near

The Lower Congo rapids, home to many restricted specialist 

species. © ROBERT SCHELLY 

Nairobi (fi ve restricted range species); the Ruvu River near 

Dar es Salaam (eight restricted range species); and the 

lower part of the Malagarasi River near its outfl ow into 

Lake Tanganyika (seven restricted range species). The 

only catchment in southern Africa with moderately high 

numbers of restricted range species is the Olifant River in 

the Western Cape that holds fi ve restricted range species, 

representing around 75% of the total number of species 

recorded in the catchment. 

3.3.4 Data Defi cient species 

Species assessed as Data Defi cient (DD) (Figure 3.8) are 

those for which the taxonomy remains uncertain, or for 

which there is insuffi cient information to make a reliable 

Figure 3.8. The distribution of Data Defi cient freshwater fi sh species across mainland continental Africa. Species 

richness = number of species per river/lake sub-catchment. 

CHAPTER 3 | FISH 63


64 

assessment of how they are impacted by threats to the 

freshwaters in their sub-catchment. The most common 

reason for this is the absence of reliable information about 

the total distribution of the species. Many species are known 

from only one or a few specimens from a single collection. 

Stiassny (1999) took a random selection of catfi shes and 

mormyrids included in the Check List of Freshwater Fishes 

of Africa (CLOFFA, Daget et al. 1984, 1986, 1991), and 

found that, for the different genera and families selected, 

25% to 80% were known only from the type series or the 

type locality from where the species was fi rst described. 

Some species may be so poorly represented by collected 

specimens that their taxonomy is unresolved. There are 

many species of Barbus, for example, where taxonomic 

complexity precludes assigning the conservation status 

as anything but Data Defi cient. Barbus eutaenia is a 

good case in point. As currently defi ned, B. eutaenia is 

widespread across much of southern and central Africa, 

but it probably represents a complex of species that 

have yet to be diagnosed and described (Tweddle et al. 

2004). This is true for numerous other poorly diagnosed, 

putatively ‘widespread’ species that, on closer taxonomic 

scrutiny and with broad geographic sampling, will likely be 

revealed to represent species complexes. 

A persistent problem presented by older, historical 

collections is that they frequently contain ambiguous 

locality information, such that the presence or absence of 

a species in a particular river system cannot be determined 

with certainty. In such cases it may be impossible to reliably 

map the distribution of these species. Even allowing for 

this underrepresentation, the map showing distribution 

of Data Defi cient fi sh species clearly indicates that data 

defi ciency is a signifi cant problem for assessments of 

African freshwater fi shes. 

The greatest numbers of Data Defi cient species are found 

in the Rift Valley lakes of eastern Africa. Lake Victoria has 

the highest proportion of Data Defi cient species for any 

of these lakes, with around 35% of the assessed species 

being classifi ed as Data Defi cient. The high numbers of 

Data Defi cient species found in these lakes results from 

a combination of factors. The lakes are rich in overall 

species numbers (see section 3.3.1), extensive areas 

have not been well surveyed, and data on the complete 

distribution and ecology of many of these species is still 

lacking. Another important factor is that the taxonomy of 

the endemic lake cichlids is notoriously diffi cult, and many 

taxonomic problems abound. 

Five or more Data Defi cient species are found in several 

parts of the Congo Basin, with higher numbers particularly 

around Malebo Pool and sub-catchments immediately 

downstream in the Lower Congo (13 to19 Data Defi cient 

species), the Upper Congo rapids ecoregion (15 Data 

Defi cient species), and the Ubangi River adjacent to the 

town of Bangui (11 Data Defi cient species). The high 

numbers of Data Defi cient species recorded from the 

Congo Basin tend to be in areas that have been relatively 

well explored. As with the Rift Valley lakes of eastern 

Africa, relatively large numbers of species have been 

collected from these regions, but data on their full ranges 

and ecology may be lacking. This is also true, to a lesser 

extent, for the Nile system, where Lake Tana and some 

parts of the Blue and the White Nile system in Sudan 

contain more than fi ve Data Defi cient species. 

Data Defi cient species are found in sub-catchments 

through most of the Lower Guinea ichthyofaunal province 

of western central Africa, and in several sub-catchments 

of western Africa, but rarely in large numbers. There are a 

few exceptions, however. In the Northern Gulf of Guinea 

drainages freshwater ecoregion, at the border of the 

Nilo-Sudan and Lower Guinea ichthyolofaunal provinces, 

the headwaters of the Cross in Cameroon contain nine 

Data Defi cient species. This region is biogeographically 

interesting, since it includes a mix of species from the two 

ichthyofaunal provinces (Reid 1989), and there is evidently 

a need to learn more about the distribution and ecology of 

many of these species. For example, Teugels et al. (1992) 

found that the number of species in the Cross River had 

previously been underestimated by as much as 73%. This 

was a particular surprise because, prior to this, the Cross 

River was thought to be one of the better-surveyed rivers 

of western central Africa. Other parts of the Lower Guinea 

province that are noteworthy for Data Defi cient species are 

the middle reaches of the Nyong River (six Data Defi cient 

species) and the Kribi River (fi ve Data Defi cient species) 

in Cameroon, the lower reaches of the Ivindo River (fi ve 

Data Defi cient species) in Gabon, and a large part of the 

Niari-Kouilou system (fi ve Data Defi cient species) in the 

Republic of Congo (Brazzaville). In western Africa, the 

middle part of the Konkouré Basin in Guinea and most 

of the Rokel Basin in Sierra Leone each have fi ve Data 

Defi cient species. 

Data Defi cient species are also found in several subcatchments 

of the Quanza and Zambezian Headwaters 

freshwater ecoregions. But, as with western Africa and 

Lower Guinea, the numbers of Data Defi cient species 

are usually low – the exceptions being a couple of subcatchments 

with fi ve Data Defi cient species, and one 

tributary to the middle section of the Quanza that has 

10 Data Defi cient species. The entire Quanza ecoregion 

(which roughly corresponds with the Quanza ichthyofaunal 

province described by Roberts (1975)) is one of the least 

explored and poorly known areas in Africa. 

In the East Coast province there is a small concentration 

of Data Defi cient species in the headwaters of the Pangani 

Basin at the border between Tanzania and Kenya (seven 

species), and in the Galana basin (in Kenya). However, the 

Tana system in Kenya covers a larger area and has more 

Data Defi cient species (fi ve to nine, with up to 32% of the

Rivers in northern Africa typically have a hydrological regime that is unpredictable and which may experience periods of intense 

fl ooding. Such conditions present a considerable challenge to the freshwater species that live in these habitats. The region is 

home to an endemic group of ’Maghreb barbs‘, which are increasingly threatened by loss of habitat. © JEAN-PIERRE BOUDOT 

assessed species being Data Defi cient in some parts of 

the basin). This illustrates that, although most rivers of the 

East Coast province are characterized by relatively low 

species numbers, considerably more research is required 

for several of these species. 

The catchments in the Atlantic Northwest and 

Mediterranean Northwest freshwater ecoregions have 

consistently low numbers of Data Defi cient species; 

however, in all these catchments, the Data Defi cient species 

represent 25% or more of the species present (and in some 

cases up to 100%). Similar patterns are seen in the Horn 

of Africa, and in the south-western Cape of Africa, where 

there are numerous sub-catchments with only one or two 

Data Defi cient species, but these represent the majority of 

the assessed species in those catchments. There are also 

areas where there is a complete lack of data for any fi sh 

species. A lack of species is unsurprising in the Sahara, 

and several other arid areas such as the Kalahari and 

Namib ecoregions in southern Africa, and the Shebelle- 

Juba ecoregion in eastern Africa (as discussed in section 

3.3.1). However, there are also sub-catchments in parts 

of the Congo main basin that have no assessed species 

(Stiassny et al. 2011), and some of these catchments are 

in undisturbed parts of the Congo forest where one would 

reasonably expect to fi nd large numbers of fi sh species. 

A similar situation exists for the Sudd wetland in southern 

Sudan. Lack of data in these cases is undoubtedly due a 

lack of surveys in these regions, indicating an urgent need 

to undertake targeted surveys before rare or undescribed 

species are extirpated (see Chapter 8). 

Some species have not been formally, scientifi cally 

described, but are nonetheless recognized by taxonomists 

as being valid. The reason they are not formally described 

is usually because taxonomists have not had the time or 

resources to publish the scientifi c descriptions. This is 

evidence of an urgent need for more support and capacity 

building for freshwater taxonomists in Africa (Stiassny 

2002; Lowenstein et al. 2011). Without a full scientifi c 

description and account of the distribution of the species 

it is not possible to ascertain their conservation status, 

and they must remain categorized as Data Defi cient. 

Numerous examples exist in the literature, and some of 

these are included in the analyses presented here but, 

according to the Red List guidelines, they are not usually 

added to the IUCN Red List unless they are thought likely 

to be threatened. 

3.3.5 Extinct species 

Three species are classifi ed as Extinct (Aplocheilichthys 

sp. nov. ‘Naivasha’; Barbus microbarbis; Salmo pallaryi); 

all three had restricted distributions and their apparent 

extinctions are attributed, at least in part, to introductions 

of alien species. Aplocheilichthys sp. nov. ‘Naivasha’ is a 

poeciliid of indeterminate taxonomy that has been reported 

as A. antinorii but, according to Seegers et al. (2003), 

is quite distinct. It has probably been extinct since the 

1970s or 1980s, following competition or predation from 

introduced species. The cyprinid Barbus microbarbis was 

known from its type locality, Lake Luhondo (=Ruhondo) 

in Rwanda, though it possibly also inhabited the small 

CHAPTER 3 | FISH 65


66 

streams fl owing into the lake. Only one specimen was ever 

caught in 1934, despite intensive sampling in the region 

(De Vos et al. 1990; Harrison and Stiassny 1999). If it is a 

valid species it is almost surely extinct, possibly as a result 

of the introduction of species of Tilapia and Haplochromis 

(De Vos et al. 1990). However, the sole type specimen was 

suspected to be a hybrid between a Varicorhinus and a 

Barbus species (Banister 1973). This hypothesis could 

be correct because, in other regions, putative hybrids 

between both genera have been identifi ed (Wamuini 2010). 

The salmonid, Salmo pallaryi, was restricted to Aguelman 

de Sidi Ali, a high altitude lake in the Atlas Mountains of 

northern Morocco, and known from at least 19 specimens 

(Delling and Doadrio 2005). The species apparently went 

extinct around 1938, probably due to the introduction 

of common carp in 1934, although Delling and Doadrio 

(2005) note that an unnamed population of trout (‘truite 

verte’) from Lake Isli, to the south-west of Aguelman de 

Sidi Ali, might be conspecifi c with S. pallaryi. 

Harrison and Stiassny (1999) and Helfman (2007) have 

discussed the possible evidence of extinction for several 

other species that are not classifi ed as such according to 

the recent IUCN Red List assessments. 

The schilbeid catfi sh Irvineia voltae is known only from 

the lower Volta Basin and is currently categorized as 

Endangered in the Red List. However, there have not 

been confi rmed reports of this species since the original 

collection before 1943. Harrison and Stiassny (1999) 

note that intensive but unsuccessful attempts were 

made to collect this species between 1961 and 1988, 

and it is possible that the species became extinct due 

to modifi cation of the river fl ow after construction of the 

Akosombo dams on the Volta River in the mid 1960s. At 

least prior to 1995, local fi shermen knew the species and 

had a name for it, but could not confi rm that they had seen 

it (DeVos 1995). More concerted surveying is necessary 

to resolve whether the species has disappeared. Besides 

the impacts from the dams, habitat quality is declining due 

to water pollution from agriculture, and possibly also from 

inadequately treated human waste. The species may also 

be affected by aquatic weeds. 

Harrison and Stiassny (1999) thought the cichlid Stomatepia 

mongo, endemic to Lake Barombi Mbo, Cameroon, might 

be extinct, because fi shermen had noted its absence 

(Reid 1991). However, the species is still extant because it 

was exported in 2007 to the USA for aquarium purposes 

(GCCA Forum 2007). Nevertheless, the fi shes of the 

crater lake, Barombi Mbo, face several serious threats. 

These include sedimentation and pollution from slashand-burn 

agriculture and oil plantations, deforestation, 

water abstraction for the neighbouring town of Kumba, 

commercial development of the region for tourism, and 

occasional fi sh kills caused by sudden releases of carbon 

dioxide contained under pressure in deep waters and 

sediments (similar to the event that occurred at Lake Nyos 

in 1986, killing more than 5,000 people and livestock) 

(Stiassny et al. 2011). Stomatepia mongo, endemic to this 

lake, is currently considered to be Critically Endangered. 

It is often noted that the largest extinction event in recent 

historical times (since 1500 AD) may have been in Lake 

Victoria, with the decline of endemic cichlid fi shes in the 

lake since the 1980s. There are indeed many species of 

cichlids endemic to Lake Victoria that are possibly extinct, 

but many of these cannot be defi nitively categorized as 

Extinct because there has been insuffi cient sampling 

or their taxonomy is not suffi ciently well described. As 

noted in section 3.3.2, many of the species in the lake are 

categorized as Data Defi cient, and there is an urgent need 

for more research and surveying of Lake Victoria fi sh fauna, 

in order to fully understand the geographic and taxonomic 

scope of this undisputed decline in cichlid species. 

Given the abundant threats to species in many parts of 

Africa (as indicated by the large numbers of threatened 

species recorded from these regions: see section 3.3.2) and 

high numbers of Data Defi cient species found throughout 

the continent (see section 3.3.4), it is reasonable to 

expect that further research and sampling throughout the 

continent might reveal evidence of extinction for several of 

these DD species. 

3.4 Major threats to species 

Deforestation, habitat loss and sedimentation 

Habitat modifi cation, through deforestation and associated 

increased sedimentation, is one of the most widespread 

threats to freshwater fi shes in Africa. The effect of this, 

even on a micro scale, has been demonstrated recently in 

the Léfi ni River, where within a relatively small stretch of 

shoreline, species composition was found to differ clearly 

between tree-covered and open areas (Ibala-Zamba 

2010). Loss of forest cover deprives many species of 

fi shes of shelter from predators, and changes the water 

temperature and hydrological regime of rivers (Brummett et 

al. 2009). Excessive sunlight and higher temperatures may 

then promote algal blooms and eutrophication. The low 

dissolved mineral and nutrient concentration of many of 

the rivers in the forested parts of Upper and Lower Guinea, 

and the Congo Basin, results in food webs dependent on 

allochthonous materials from the forest. The removal of 

riparian forest can affect peak fl ow fl ooding events, which 

impacts the freshwater species present and the human 

communities within the catchments (Bradshaw et al. 2007, 

2009; Brummett et al. 2009; Farrell et al. 2010). Thus, 

deforestation can signifi cantly affect the ecohydrology 

of river systems (and lakes, such as the crater lakes of 

western Africa (Stiassny et al. 2011)). Deforestation results 

in signifi cant increases in sedimentation as delicate forest 

soils, which are easily eroded, are exposed and washed

into streams, rivers, and lakes. The sediment covers 

submerged surfaces, reducing suitable habitat for breeding 

and feeding of many fi sh populations. The increased 

turbidity can clog the gills of fi shes and suffocate their 

eggs (Roberts 1993), as well as reducing the light levels 

so that submerged plants cannot photosynthesize and so 

die, exacerbating eutrophication of the waters. 

Expansion and intensifi cation of logging and agriculture 

are common causes of deforestation. Threats from 

deforestation are particularly strong and widespread in 

the Upper and Lower Guinea provinces, and in the Congo 

Basin, given that these encompass the last remaining 

extensively forested regions on the continent. Smith et 

al. (2009) note that in western Africa (which includes the 

Upper Guinea and Nilo-Sudan ichthyofaunal provinces), 

deforestation is especially prevalent along the banks of 

the Volta, Niger, and Senegal rivers. Some examples of 

fi shes in the Upper Guinea region that are impacted by 

deforestation are discussed in section 3.3.2. The central 

African region has already lost an estimated 46% of its 

rainforest to logging and conversion to agriculture, and 

continues to lose forested watershed at an average rate of 

7% per year (Revenga et al. 1998). The Kasai, Sanga, and 

Upper Congo freshwater ecoregions are some of the more 

seriously impacted areas in terms of ongoing deforestation, 

while the Lower Congo has been almost entirely deforested 

for many decades (Stiassny et al. 2011). Deforestation is a 

major threat in many parts of the Lower Guinea province, 

and much of this is associated with logging (e.g., in the 

Nyong (Cameroon), the Ogowe/Ivindo system (Gabon), 

and Kouilou/Niari systems (Republic of Congo)). However, 

as well as slash-and-burn agriculture, charcoal production, 

banana, rubber, and oil palm plantations are other major 

drivers of deforestation and associated sedimentation 

through Lower Guinea (especially in Cameroon), and in 

some parts of the Congo Basin (Brummett et al. 2009). 

Extremely biodiverse rainforest along the Cameroon 

coast, roughly from the Ndian to the Kribi (Kienké) rivers, 

has been converted to oil palm, as have parts of the Upper 

Congo freshwater ecoregion, and there are plans for 

development of oil palm plantations around Lake Tumba 

(Brummett et al. 2011). Deforestation has also taken place 

to allow for the development of eucalyptus plantations 

along the coast of the Republic of Congo and Cabinda. 

Eucalyptus is mainly used for building materials and for 

fi rewood and charcoal. Deforestation specifi cally for the 

production of fi rewood and charcoal is a more serious 

problem for parts of western and central Africa, especially 

near areas of urban development, where remnant riparian 

vegetation is particularly under threat (Smith et al. 2009; 

Brummett et al. 2011). 

Deforestation for logging also opens up large tracts of 

forest for further exploitation, for example, by mining and 

agriculture ventures, bush meat hunting, and settlement. 

Mining has signifi cantly contributed to further habitat 

Mining, such as observed here in the East Nimba Forest 

Reserve in Liberia, has signifi cantly contributed to habitat 

loss and high levels of sedimentation in many regions across 

Africa. © K.-D.B. DIJKSTRA 

loss and high levels of sedimentation in many regions. 

Small-scale alluvial mining, larger commercial mines, and 

extraction of sand or clay have impacted rivers basins in 

parts of southern, western, and central Africa (Darwall et 

al. 2009; Smith et al. 2009; Brooks et al. 2011). Mining 

is especially common in the Congo, Sanga, and Kasai 

basins. Land conversion for agriculture impacts riparian 

forests, as well as many other habitats. In eastern Africa, 

the high number of threatened fi shes in the Malagarasi 

Basin is due to encroachment of agriculture into the 

wetlands (Darwall et al. 2005). Similarly, the high number 

of threatened species in the Ruvu River, draining to the 

coast of Tanzania, probably results from many regionally 

endemic species being found in areas at high risk of 

habitat modifi cation. 

Livestock are frequently placed on the cleared land, causing 

overgrazing, and these poorly managed processes of land 

clearing and grazing result in accelerated soil erosion and 

increased sedimentation. The Ubangi River in central Africa 

is so severely impacted by sedimentation from mining and 

agriculture in the region of Mpoko that the reduced river 

depth prevents shipping for four or fi ve months in most 

years (Brummett et al. 2009). 

Not surprisingly, loss of riparian habitat and deterioration 

of freshwater ecosystems are greatest in areas of high 

human settlement. For example, several species of fi shes 

are impacted by habitat loss in the heavily populated lower 

Ogun Basin in Nigeria, as well as in the northern parts of 

Lower Guinea, and close to the large cities of Kinshasa 

and Kisangani in the Congo Basin (Stiassny et al. 2011). In 

several parts of the Congo Basin (particularly the eastern 

part of the basin and in the vicinity of the Sangha; see 

Brummett et al. 2011) and Upper Guinea, war and civil 

unrest have displaced local communities into previously 

undisturbed regions of forest, with these communities 

often settling along waterways (Thieme et al. 2005), with 

consequent loss of forest cover. 

CHAPTER 3 | FISH 67


68 

Pollution 

Water pollution is a problem in many parts of Africa. The 

impacts of pesticides and fertilizers from agriculture on 

freshwater systems have been reported in all regional 

studies (Darwall et al. 2005, 2009; Smith et al. 2009; García 

et al. 2010a; Brooks et al. 2011). The effects of pollution 

are usually also coupled with impacts from increased 

sedimentation caused by soil erosion, and frequently 

result in eutrophication of the lakes and rivers (e.g., the 

Malagarasi Basin, which is impacted by agriculture 

(see above)). Pollution from mining is a serious threat in 

the regions where small-scale or commercial mining is 

prevalent (see above). The use of pesticides in vector control 

programs for diseases like malaria, schistosomiasis, and 

trypanosomiasis (e.g., in parts of western Africa (Smith et 

al. 2009)) may also impact fi shes, with low doses possibly 

compromising their physiology and behaviour. The use 

of such pesticides as a method of fi shing is an additional 

problem in central Africa. 

Organic pollution from human and domestic waste 

threatens fi shes in all areas where there are sizeable 

settlements. Pollution from oil exploration, factories or 

other urban industries, cars in the cities, and from boat 

traffi c on rivers impacts the freshwater systems, especially 

those close to large cities, such as Kinshasa and Lagos. 

Pollution from oil exploration, and associated loss of 

habitat, specifi cally threatens several restricted range 

species in the Niger Delta, and may pose a threat to 

species in coastal freshwater systems of Gabon, Cabinda, 

the Republic of Congo and Angola. 

Dams 

Some 1,207 dams have been constructed on small and 

large rivers of Africa; at least 135 of these are classifi ed as 

large dams (> 500,000m³) (FAO 2010) (see also Chapter 

1, Figure 1.3). The greatest concentrations of dams, 

and some of the largest, are in the Maghreb province of 

northern Africa, much of western Africa, and Zimbabwe in 

southern Africa. Dams prevent the longitudinal migration 

of fi sh, and create lake-like conditions upstream that are 

uninhabitable for many of the riverine fi shes that were 

originally present. These lake reservoirs also attract 

the attention of anglers for the introduction of exotic 

lacustrine species that may become invasive in the lake 

environment, especially in southern Africa. Downstream 

fl ow and sediment load may be changed to such an 

extent that the habitats immediately below the dam are 

also unsuitable for habitation by previously native fi shes. 

The overall impact of dams may be severe, as noted 

for the Aswan Dam (see section 3.3.2). The potential 

for future development of hydropower projects in Africa 

is also large, including plans for some very large dams, 

such as the 39,000MW ‘Grand Inga’ dam proposed for 

development on the lower section of the Congo River 

by 2025 (see Brummett et al. 2011) (but see Chapter 1, 

section 1.2.2.1). 

Dams, such as the Akosombo Dam on the Volta River in 

Ghana, will have a signifi cant impact on freshwater species. 

These impacts need to be evaluated before construction, 

and operation procedures, for new dams are approved. 

© WILLIAM DARWALL 

River channelization and water abstraction 

The geomorphology and fl ow of many rivers is affected 

by channelization (often for irrigation or inter-basin 

transfer of water) and abstraction of water to supply 

agriculture, and industrial and domestic consumption. 

In South Africa, inter-basin transfer schemes of water 

have facilitated the spread of introduced species (Darwall 

et al. 2009), and may also allow the migration of native 

species to new basins beyond their normal range, with the 

possibility of interbreeding between populations that are 

normally isolated. This may result in detrimental genetic 

homogenization of the populations. 

Water abstraction is a threat particularly in arid areas that 

have human settlements, such as northern and southern 

Africa (see section 3.3.2). In western Africa, water 

abstraction (coupled with climate change), has severely 

impacted the wetlands of Lake Chad, greatly reducing the 

surface area of the lake from 25,000km² in the early 1960s 

to around 1,350 km² in 2001 (García et al. 2010a). When 

water removal signifi cantly disturbs the environmental 

fl ow of a stream or river, this may pose a signifi cant threat 

to any endemic species whose range is restricted to the 

The geomorphology and fl ow of many rivers is affected by 

channelization, as is the case here on the Kou stream in 

Burkina Faso. © TIMO MORITZ

The high diversity of fi sh communities, such as seen here on 

the Malagarasi, Tanzania, are often impacted when dams are 

constructed. © JOHN FRIEL 

area where the water removal is occurring. Small dams 

or weirs, river channelization, and water abstraction may 

all operate together in some places, where the weirs are 

installed to divert water and create deeper pools from 

which it is easier to extract the water by pump. 

Overfi shing 

Overfi shing is a major threat to many species in the Great 

Lakes of the African Rift Valley, such as in Lake Malawi 

(see section 3.3.2), particularly where fi sheries are focused 

along the migration routes of species as they move from 

the lake into river mouths to spawn. Smith et al. (2009) 

also note that many freshwater bodies in western Africa 

are overfi shed, particularly the Volta. Those authors report 

that there has been a disappearance of larger species 

in some western African rivers such as the Oueme, as a 

result of sequentially fi shing down the food web. Allan et 

al. (2005) note that this decline in fi sh size is accepted in 

parts of Africa, due to some regional preference for small 

fi sh in the cuisine. García et al. (2010b) note that Lates 

niloticus, Anguilla anguilla, Barbus bynnii, Hydrocynus 

forskahlii, and Alestes dentex are unsustainably harvested 

in northern Africa. Threats from poorly managed fi sheries 

(overharvesting or the use of small mesh, unselective fi shing 

gear, fi sh poisons and explosives) have also been reported 

for the Congo Basin, particularly in areas such as Malebo 

Pool, Lake Tumba, and Mai N’dombe. Some fi sh species 

are also the focus of commercial and artisanal fi sheries for 

the aquarium trade, for example, some killifi shes in Lower 

Guinea (Stiassny et al. 2011) and Arnoldichthys spilopterus 

(see section 3.3.2). 

Invasive species 

Invasive species are a problem in many parts of Africa, 

and their success has been aided by habitat modifi cation 

and the development of dams (see above). The impact 

on haplochromine cichlids and the introduced Nile perch 

(Lates niloticus) to Lake Victoria in East Africa has been 

extensively documented (see section 3.3.2 and 3.3.5). In 

eastern Africa, introduced tilapiine and haplochromine 

Arnoldichthys spilopterus (VU), the Niger tetra, is endemic to Nigeria, where it is restricted to the lower Ogun and lower Niger 

rivers. © TIMO MORITIZ 

CHAPTER 3 | FISH 69


70 

Drought is a serious problem for many parts of Africa, with 

many lakes drying out, such as the Mare Bali water hole in 

Pedjari National Park, Benin, pictured here. © TIMO MORITZ 

cichlids are themselves a threat to a cyprinid, Varicorhinus 

ruandae, in Lake Luhondo (a small lake in the northern part 

of Rwanda), through competition and predation (De Vos et 

al. 1990). 

Invasive species pose the greatest recorded threat to 

fi shes in southern Africa, mainly coming from introduced 

European or North American species (e.g., Micropterus 

dolomieu; Oncorhynchus mykiss and Salmo trutta; also see 

Species in the Spotlight– Tilapia in eastern Africa – 

a friend and foe), and from invasive species of the cichlid 

genus Oreochromis. Introduced mosquitofi sh (Gambusia) 

have had very signifi cant impacts on native species in 

northern Africa (see section 3.3.2). The water hyacinth 

(Eichhornia crassipes) is one of the most widespread 

invasive species in Africa, presenting a considerable threat 

to freshwater ecosystems in most of sub-Saharan Africa. 

The economic impacts of the water hyacinth are estimated 

at USD 20-50 million every year in seven African countries, 

and may be as much as USD 100 million annually across 

all of Africa (Chenje and Mohamed-Katerere 2006) (see 

Species in the spotlight – Water hyacinth, a threat 

to the freshwater biodiversity). 

Climate change and extreme events 

Fish faunas already weakened by many of the threats 

noted above are especially susceptible to the impacts of 

natural disasters, such as drought, and to climate change. 

According to García et al. (2010b), natural disasters are 

the second most serious cause of decline for almost two 

thirds of the freshwater fi sh in northern Africa. Drought is a 

serious problem in parts of northern and southern Africa, 

where many once permanent streams have become 

seasonal or have dried completely. Lake Chad, in western 

Africa, was reduced to 5.4% of its surface area between 

the 1960s and 2001 (see above), and it is estimated that 

50% of this reduction was caused by changes in climate 

patterns (Pietersen and Beekman 2006) (see also Chapter 

1, Figure 1.5). Climate change is also expected to impact 

the forested regions of Africa, although the precise nature 

of these impacts is unclear (Schiermeier 2008; Thieme 

et al. 2010; Brummett et al. 2011). It is expected that, 

by the 2050s, more than 80% of Africa’s freshwater fi sh 

species may experience hydrologic conditions that are 

substantially different from the existing conditions. A more 

detailed account of the impacts of climate change are 

given in Chapter 8, this volume. 

In conclusion, there are many types of threat that are 

impacting the freshwater fi sh fauna of Africa. In most 

cases, decline in population size and distribution of any 

species is a product of a combination of these factors, 

rather than the result of any single threat. Harrison and 

Stiassny (1999) discuss how several combined threats 

resulted in the decline of many of the cichlid species of 

Lake Victoria in the 1980s (see also Chapter 1, Box 1.1). 

A more recent example is provided by the calamitous 

decline of the European eel (Anguilla anguilla) (Critically 

Endangered) throughout its range. In northern Africa, 

this decline may be attributed to the combined effects of 

overfi shing of silver eels in coastal waters, the impacts of 

parasitic pathologies, pollution, construction of dams and 

water abstraction, and gravel extraction from river beds 

(García et al. 2010b). Similarly, the decline of Aphanias 

saourensis to Critically Endangered status in northern 

Africa is attributable to a combination of factors including 

groundwater abstraction, pollution, and introduction of 

invasive species (see section 3.3.2). 

3.5 Research actions required 

This study highlights specifi c patterns of the distribution 

and conservation status of fi shes throughout the continent, 

and has identifi ed some conservation recommendations 

(see section 3.6) and priorities. However, the study has 

also confi rmed the opinion of Lundberg et al. (2000) that 

signifi cant gaps in our knowledge of this fauna still exist. 

Considerable additional research is required to provide 

basic baseline data for several potentially biodiverse 

regions to support conservation management. The lack 

of knowledge of even the most basic distributional and 

ecological data, and the need for further research on the 

fi shes of large parts of Africa (in particular, the Congo 

Basin), is well exemplifi ed by the increased knowledge 

resulting from the recent study on the ichthyofauna of the 

Léfi ni River (as reported above), a tributary draining from 

the west into the middle Congo (Ibala-Zamba 2010). 

Where information is available on species’ presence and 

distributions within a catchment, there is, however, often 

very little additional information about the ecology of each 

particular species. In the absence of such information it is 

very diffi cult to accurately assess the conservation status of 

the species, and to make suitable conservation decisions. 

A major challenge is to accumulate data that can help 

reduce the total number of species that are classifi ed as

Data Defi cient (514 species, 18% of all assessed species) 

(see Chapter 8 for discussion of prioritising fi eld work to fi ll 

these knowledge gaps). 

The impact of climate change on freshwater ecosystems 

of Africa is an important concern, but one which may be 

mitigated through a better understanding of the resilience 

of species to change, and through proper management 

of freshwater resources (see chapter 8, section 8.6.1). 

However, this also requires further research on the diversity 

and ecology of the species present, the environmental 

fl ows required to support this biodiversity, and additional 

meteorological and hydrological data. These features 

of climate change must then be considered alongside 

other threats (for example, dam construction, overfi shing, 

or deforestation) in order to predict the overall impact. 

Spatial modelling is useful for all these studies, although 

interpretation of the results is often diffi cult for aquatic 

species. The diffi culties lie mainly in the complexities of 

modelling characteristics of underwater habitats, and 

in identifying routes of dispersal within catchments, 

and barriers to this dispersal both within and between 

catchments. 

The best instrument for evaluating changes in the 

ichthyofauna of Africa is long-term, standardized 

monitoring. This will detect shifts in species composition, 

as well as changes in biomass and local incidences of 

fi shing down the food web. Standardized monitoring 

should also be implemented as a routine step before any 

large infrastructure is developed on or along the waterway. 

In many regions, however, political and socio-economic 

instability, logistical problems, and lack of fi nances and 

taxonomic expertise combine to hamper even the most 

basic studies, including monitoring programmes. If these 

problems of infrastructure, training and fi nance can be 

remediated, then hopefully the recommended studies of 

species and population diversity and ecology to monitor 

the health of the fauna can be initiated. 

3.6 Conservation recommendations 

The fi ndings of this assessment confi rm that the freshwater 

fi shes of Africa are signifi cantly threatened in many parts 

of the continent, and it is reasonable to assume that even 

greater stress will be exerted on this fauna in the future. 

Nevertheless, it may be diffi cult for policy makers to set 

conservation recommendations as priorities when there 

are many other urgent issues associated with ensuring that 

people are guaranteed an acceptable standard of living. The 

many actions required to meet basic human requirements 

may appear to be at odds with the objectives of freshwater 

biodiversity conservation. There is, however, a need to 

The importance of inland fi sheries to local economies can been seen by this thriving fi sh market on the banks of the Congo 

River, at Mbandaka, D. R. Congo. © R. SCHELLY 

CHAPTER 3 | FISH 71


72 

The banded distichodus, Distichodus sexfasciatus (LC), is widespread throughout central Africa. A beautiful species such as 

this is collected for the aquarium trade – it is also an important food fi sh. © SAIAB/ROGER BILLS 

protect and sustainably manage freshwater ecosystems to 

deliver the many ecosystem services that are also essential 

to people. At the most basic level, effectively functioning 

aquatic ecosystems with healthy fi sh populations that 

can be sustainably exploited are to the benefi t of all. But 

recent studies, such as that by Vörösmarty et al. (2010), 

have shown that the need for sustainable management of 

freshwater resources goes far beyond ensuring biodiversity 

conservation and food security through reliable fi sheries. 

Their study has shown that the provision of adequate 

human water security in wealthy nations (such as in parts 

of Europe and North America) has only been possible by 

massive fi nancial investment in water technology to offset 

the impacts of threats, but this investment is not possible 

in less wealthy nations, where biodiversity and human 

water security remain vulnerable. In much of Africa, the 

sustainable management of freshwater resources and 

biodiversity offers a cost effective and environmentally 

sustainable alternative. 

Habitat loss or modifi cation ranks among the primary 

threats for extinction of freshwater fi shes not only in Africa 

(see section 3.4) but also worldwide (Harrison and Stiassny 

1999) (see Chapter 1, this volume). Adequate protection 

and management of freshwater and riparian habitats is, 

therefore, a key recommendation for the conservation of 

freshwater fi shes. Numerous nominal parks and reserves 

exist in Africa (e.g., see Stiassny et al. 2011) but, in practice, 

many are focused on terrestrial habitats rather than the 

freshwater ones that exist within them or along their 

borders, where they are especially vulnerable (Abell et al. 

2007; Allan et al. 2010). For example, it is not uncommon 

that fi shing rights are still exerted within protected areas 

or parks. Development of parks and protected areas 

that specifi cally address the conservation challenges for 

rivers, lakes and wetlands will be important for the future 

conservation of Africa’s freshwater fi shes. For example, 

in central Africa the Ministry of Environment for D. R. 

Congo and the Institut Congolais Pour la Conservation 

de la Nature (ICCN) initiated a country-wide biodiversity 

assessment to identify priority areas for conservation, 

and have identifi ed 30 wetland priority areas (Thieme et 

al. 2008). 

Lake Malawi National Park was established in 1980, 

especially aimed at protecting part of Lake Malawi’s 

unique fi sh fauna; nevertheless, the scope of the park is 

quite limited, and more initiatives are required to reduce 

the high levels of threat, such as from overfi shing. To this 

end, special programmes have been implemented, such 

as the ‘chambo restoration strategic plan’ to protect one of 

the more important taxa (Oreochromis) in the lake fi shery.

Allan et al. (2010) discuss the need for a new conceptual 

framework for developing and managing protected areas 

that accounts for the need to conserve ecosystems while 

also allowing for the diverse requirements of people. This 

concept is based on Abell et al.’s (2007) recommendation 

for a multiple-use zoning framework, where focal areas 

for freshwater conservation are embedded in critical 

management zones, and these, in turn, are embedded in 

catchment management zones. Various other programs, 

ranging from large-scale management of catchments to 

species-specifi c or site-specifi c programmes, have been 

shown to be important for conservation of freshwater 

biodiversity and provision of ecosystem services. García et 

al. (2010b) noted that Integrated River Basin Management 

(IRBM) is a key conservation action required to stop 

species decline in northern Africa. Cross (2009) described 

the catchment-scale actions of the Pangani River Basin 

Flow Assessment Initiative (FA), co-ordinated by the IUCN- 

Pangani Basin Water Offi ce (PBWO). Tweddle et al. (2009) 

describe some successful projects and conservation 

recommendations in southern Africa directed at diverse 

scales, from whole landscapes to local sites and individual 

species. These include eradication of invasive species and 

limitation of the use of alien invasive species in aquaculture 

programmes. Such actions, at both the site and catchment 

scales, are covered in more detail in Chapter 9. 

Another recommendation is that reliable fi sheries catch 

statistics are maintained and made available. In many 

areas, little information is available on species composition 

and catch quantities. This is directly related to the lack 

of inventories and identifi cation keys in many areas 

and a chronic lack of taxonomically trained personnel. 

Trained local staff would then assimilate and translate 

the knowledge of local fi shermen and make it available 

to resource managers and scientists to inform decisions 

and policy. 

On a more general note, ‘Payment for Ecosystem Services’ 

(PES) programs are mechanisms where the benefi ciaries of 

freshwater ecosystem services pay for the supply of these 

services (Forsland et al. 2009). For example, downstream 

communities that receive clean water for domestic and 

agricultural use pay the upstream communities to conserve 

and manage the habitats so they continue to supply clean 

and plentiful water. Conservation stewardship agreements 

are another form of PES scheme, where trust funds are set 

up to supply local communities with fi nancial incentives 

(for example, money for new jobs, or healthcare) in return 

for agreement that they manage their freshwater resources 

sustainably. 

Many of the conservation recommendations discussed 

above will be impossible if not backed by adequate 

development of policy and enforcement of regulations 

and laws (Smith 2010). However, many governmental 

bodies lack the fi nancial and logistical means to enforce 

existing laws and rules, and therefore mechanisms must 

be put in place to assist in this process. The Convention 

of Biological Diversity (ratifi ed by several African 

countries) and the Ramsar Convention (Landenbergue 

and Peck 2010) may help with the development of policy 

and laws. The Convention was supported recently by the 

agreement at the 10th Conference of the Parties to the 

Convention on Biological Diversity (CBD-COP10, held at 

Nagoya in November 2010) that 17% of terrestrial and 

inland water areas globally should be protected, and that 

’By 2020 the extinction of known threatened species 

has been prevented and their conservation status, 

particularly of those most in decline, has been improved 

and sustained.’ 

In conclusion, our objective for the future must be to 

effectively conserve and manage African freshwater fi sh 

biodiversity, at the same time as supporting the livelihoods 

and economies of the people who are dependent on these 

resources and are the critical stakeholders in ensuring 

sustainable management practices. This can only be 

achieved by multi-disciplinary approaches to scientifi c 

research, development of tools for the application of 

that research to conservation and management, and the 

implementation of policy that supports recommendations 

made as a consequence of all of the above (Farrell 2010; 

Smith 2010). 

CHAPTER 3 | FISH 73

CHAPTER 3 | SPECIES IN THE SPOTLIGHT 

74 

Species in the spotlight 

The Congo blind barb: Mbanza- 

Ngungu’s albino cave fi sh 

The enigmatic, Congo blind 

barb, Caecobarbus geertsii, 

was scientifi cally described 

by Boulenger (1921), based 

on four specimens collected in 1920, 

from the ‘Grottes de Thysville’ in 

the Lower Congo region (Roberts 

and Stewart 1976) of D. R. Congo. 

It was the fi rst African cave fi sh to 

be discovered. The species is locally 

referred to as ‘Nzonzi a mpofo’ in 

Kikongo (the local Ndibu dialect) 

which literally means ‘blind barb’. 

Although the eyes are not visible, 

they are present. They are deeply 

embedded in the head, lack a 

lens, and have only a rudimentary 

retina and optical nerve (Gerard 

1936). Nevertheless, Thinès (1953), 

contrary to Petit and Besnard 

(1937), notes that the species moves 

away from light, demonstrating a 

typical photonegative reaction due 

to the existence of extra-ocular 

photosensitivity. 

The species also lacks 

pigmentation (Boulenger 1921; 

Heuts 1951) and is considered a 

true albino, as placing live animals 

under light for more than one month 

does not result in development of 

pigment (Gerard 1936). However, 

Poll (1953) reported the presence of 

melanophores in a specimen kept 

for seven months in an aquarium. 

The lateral vein creates a vivid red 

Vreven, E.¹, Kimbembi ma Ibaka, A.² and Wamuini Lunkayilakio, S² 

A live specimen of Caecobarbus geertsii from the cave ‘Grotte de Lukatu’, D. R. Congo. © ROYAL MUSEUM FOR CENTRAL AFRICA 

band along the lateral line. Below 

the operculum the gills are visible as 

a purplish region, and the intestinal 

region is visible through the 

abdomen (Petit and Besnard 1937). 

Heuts (1951) estimated longevity 

at nine to 14 years; Proudlove and 

Romero (2001) stated the lifespan 

may exceed 15 years, but this needs 

to be confi rmed. The species reaches 

a maximum size of 80 to 120mm 

total length, based on the largest 

specimen housed at the Royal 

Museum for Central Africa. 

Following explorations of 

several caves in 1949, Heuts (1951) 

and Heuts and Leleup (1954) 

recorded C. geertsii from seven 

caves around Mbanza-Ngungu 

(formerly Thysville), situated on the 

western slope and the top of the 

Thysville mountain ridge (Monts 

de Cristal: 750 to 850m elevation). 

One population was reported as 

extirpated by the exploitation of 

limestone between 1930 and 1935 

(Leleup 1956; see also Heuts and 

Leleup 1954). Indeed, a visit to the 

cave site in 2005 found it to have 

completely disappeared following 

excavation of the slope. 

The presence of C. geertsii in at 

least four of the other caves reported 

by Heuts and Leleup (1954) has 

been confi rmed by recent surveys by 

Kimbembi (2007) and the authors. 

1 Royal Museum for Central Africa, Vertebrate Section, Ichthyology, Leuvensesteenweg 13, B-3080 Tervuren, Belgium 

2 Institut Supérieur Pédagogique de Mbanza-Ngungu, Bas-Congo, Laboratoire de Biologie, Democratic Republic of Congo 

Statistical population surveys 

have been impossible because the 

subterranean habitat is extensive 

and diffi cult to sample (Heuts 

1951); however, a gross population 

estimate for the seven caves 

reported by Heuts and Leleup (1954) 

would be about 7,000 individuals 

(based on information supplied by 

those authors). Kimbembi (2007) 

discovered seven more caves with at 

least small populations of C. geertsii, 

although no population estimations 

have been made for these. 

Heuts (1951) and Heuts and 

Leleup (1954) previously considered 

C. geertsii to be present in only two 

upper tributaries of the Kwilu Basin 

(an affl uent of the Lower Congo), 

namely the Fuma and the Kokosi. 

One of the new caves that Kimbembi 

(2007) identifi ed as holding C. 

geertsii is on the Tobo River, another 

affl uent of the Kwilu Basin. Lévêque 

and Daget (1984) and Banister (1986) 

also reported the species from the 

Inkisi Basin, but at the time had no 

evidence for this. However, inferred 

from mapping of the new cave 

localities identifi ed by Kimbembi 

(2007), the species’ presence in 

the Inkisi River basin seems to be 

confi rmed by two of them – one on 

the Tubulu River and another one 

on the Uombe or possibly the Kela 

River, a tributary to the Uombe. The

presence of C. geertsii in D. R. Congo, 

as reported by Lévêque and Daget 

(1984), is incorrect. Thus, the entire 

distribution area of the species is 

about 120km 2 . Heuts (1951) noted 

important differences between the 

different populations of C. geertsii 

in the Kwilu basin. Populations 

present in affl uents of the Kokosi 

River have an opercular guanine 

spot which may cover one third of 

the operculum (in addition to a few 

other guanine spots and marks). 

This spot is absent in all other 

populations (affl uents of the Fuma 

River). Furthermore, within one 

cave the population has a serrated 

dorsal spine, which was not found in 

all other populations examined by 

Heuts (1951). 

Traditionally, caves are sacred 

in the area (Laman 1962) and, as a 

result, access to most of the caves is 

restricted still today. A law, passed 

on 21 April 1937, protected C. geertsii 

from all hunting and fi shing, except 

for scientifi c purposes (Frenchkop 

1941, 1947, 1953; Duren 1943). The 

species was added to the CITES 

Annex II (on 6 June 1981), resulting 

in an international trade restriction 

which means that the species cannot 

be traded without appropriate 

export and import permits. C. geertsii 

is still the only African freshwater 

fi sh species on the CITES list. The 

IUCN Red List status of C. geertsii 

is Vulnerable (VU), due to a limited 

geographic range and a decline in 

the area and quality of its habitat 

(Moelants 2009). 

Caecobarbus geertsii was found in 

only seven of the 45 caves explored 

by Heuts and Leleup in 1949. This 

indicates, according to Heuts 

(1951) and Heuts and Leleup (1954), 

that caves must have a specifi c 

combination of ecological conditions 

if they are to be populated by C. 

geertsii, and they summarised the 

following conditions: 

1. high calcium bicarbonate 

concentrations in the water; and 

2. a distinct periodicity of the 

subterranean river fl ow regime 

through the caves. 

Due to this periodic inundation 

of the caves inhabited by C. 

geertsii, other typical cave animals, 

such as terrestrial insects, are 

absent. Therefore, C. geertsii is 

entirely dependent on an external, 

exogenous, food supply to the caves 

during the rainy season with, as a 

result, important fl uctuations in 

food resources between seasons. 

Moelants (2009) states that 

the species may feed on small 

crustaceans living in the caves, 

but this needs to be confi rmed. 

Consequently, growth is extremely 

slow, and all further available data 

suggest a very low reproduction rate, 

justifying protection measurements. 

A visit to the Kambu cave by the 

authors in August 2009 failed to fi nd 

the species, although its presence 

had been reported by Kimbembi 

(2007). However, several individuals 

of at least one species of Clarias (± 

200mm standard length) were found 

in the different isolated pools. This 

observation suggests predation of 

C. geertsii by species of Clarias, as 

previously proposed by Heuts and 

Leleup (1954) and by Leleup (1956). 

Caecobarbus geertsii has, in the 

past, been traded as an aquarium 

fi sh, with large numbers having 

been exported to industrialized 

nations. Collection pressure should 

have been reduced through listing 

under CITES; however, a CITES 

certifi cate was issued to import 

1,500 individuals to the Unites 

States (Proudlove and Romero 

2001). Three other primary threats 

to the species were identifi ed by 

Brown and Abell (2005): changes 

in hydrology of the small rivers 

feeding the caves; increasing 

human population; and associated 

deforestation (Kamdem Toham 

et al. 2006). Since 2003, with the 

attenuation of the political situation 

in D. R. Congo and the rehabilitation 

of the Matadi-Kinshasa road, there 

has been a signifi cant infl ux of 

rural people towards Mbanza- 

Ngungu. Consequently, land use has 

increased around Mbanza-Ngungu 

for buildings as well as agriculture. 

One cave is now used as a quarry, 

with consequential loss of the 

Caecobarbus population (Leleup 

1956; Poll 1956; and see above), and 

others are at risk of collapse due 

to human disturbance (Kimbembi 

2007; Moelants 2009). Agriculture is 

practiced preferentially in the valleys 

near to the caves but may also occur 

on the hillside slopes surrounding 

and covering the caves, leading to 

increased erosion and landslides. In 

the past, these areas were covered 

with lowland rainforest and 

secondary grassland (White 1986), 

limiting erosion. Further research 

and conservation initiatives in the 

fi eld are necessary if this unique 

species of fi sh is to survive. 

Land use around the entrance of the ‘Grotte de Lukatu’, with subsequent landslides 

visible (9 March 2007). The entrance to the cave is directly below the largest trees 

in the middle of the photograph. © ROYAL MUSEUM FOR CENTRAL AFRICA 


75


76 


Tilapia in eastern Africa – a friend and foe 

Tilapia form the basis for 

much of the aquaculture 

industry that is important 

to so many people across 

Africa. Its success as a commercially 

fi shed and cultured species is 

attributed to several characteristics: 

its ability to establish and occupy 

a wide variety of habitats; its wide 

food spectrum from various trophic 

levels (Moriarty 1973; Moriarty 

and Moriarty 1973; Getachew 1987; 

Khallaf and Aln-Na-Ei 1987); high 

growth rate; large maximum size; 

and high fecundity (Ogutu-Ohwayo 

1990). All of these factors accord O. 

niloticus with great competitiveness 

over other tilapia, which can 

become a problem where they have 

been introduced, or escaped, to 

areas outside of their native range. 

Aquaculture is also one of the most 

common sources of invasive species 

in many parts of the world, and the 

famous Nile tilapia (Oreochromis 

niloticus niloticus), in particular, is 

recognised as a signifi cant threat 

to other native fi sh species. The 

popularity of tilapia in Africa is 

indicated by their high market 

value and, consequently, the high 

fi shing pressure in most lakes and 

rivers (Abban et al. 2004; Gréboval 

et al. 1994). 

The Nile tilapia 

Eastern Africa is endowed with 

six sub-species of Nile tilapia: O. 

niloticus niloticus (Linnaeus, 1758), 

originally from the White Nile 

Basin but now widely introduced 

elsewhere; O. niloticus eduardianus 

(Boulenger, 1912) in Lakes Edward, 

Kivu, Albert and George; O. 

niloticus vulcani (Trewavas, 1933) in 

Lake Turkana; O. niloticus sugutae 

Trewavas, 1983 in the Suguta 

The Nile tilapia, Oreochromis niloticus, 

(LC), a highly favoured species for 

aquaculture. © LUC DE VOS 

river basin; O. niloticus baringoensis 

Trewavas, 1983 in Lake Baringo; 

and one other recently discovered 

(Nyingi et al. 2009), but still 

undescribed subspecies from the 

Lake Bogoria Hotel spring near 

the Loboi swamp, between Lake 

Baringo and Bogoria in the Kenyan 

Rift Valley. 

Oreochromis niloticus was 

introduced to Lake Victoria for 

the purpose of improving tilapia 

fi sheries in several phases between 

1954 and 1962, due to decreasing 

stocks of native tilapia species 

O. esculentus and O. variabilis. 

Oreochromis niloticus rapidly 

colonized the entire lake and by 

the end of the 1960s was well 

established in inshore habitats 

(Mann 1970; Ogutu-Ohwayo 1990; 

Twongo 1995). It is thought that 

the introduction of O. niloticus 

caused the disappearance of the 

two native tilapia species (O. 

variabilis and O. esculentus) from 

the main part of the lake – O. 

esculentus having once represented 

the bulk of the fi sheries in the lake. 

It was initially hypothesised that 

hybridization with subspecies of 

O. niloticus was the main driver of 

the decline of O. variabilis and O. 

esculentus, because O. niloticus is well 

known for its ability to hybridize 

Nyingi, D.W.¹ and Agnèse, J.-F.² , ³ 

with other tilapiines (Welcomme 

1988; Mwanja and Kaufman 1995; 

Rognon and Guyomard 2003; 

Nyingi and Agnèse 2007). However, 

the competitive superiority of 

O. niloticus subspecies over the 

two former native species was 

demonstrated to be the most likely 

contribution for their extinction 

(Balirwa 1992; Agnèse et al. 1999). 

Tilapia and aquaculture 

The greatest limitation to 

development of aquaculture in 

eastern Africa has been fi nancial, 

with all new activities in the 

sector initiated and dependent on 

foreign fi nancing. In Kenya, the 

government has stepped up efforts 

to promote aquaculture under the 

Economic Stimulus Programme. 

The government’s intention has 

been to highlight fi sh farming as 

a viable economic activity in the 

country by raising the income of 

farmers and other stakeholders in 

the fi shing industry. The project, 

worth 1,120 million Kenya shillings 

(EUR 10.67 million) was launched 

by the Ministry of Fisheries 

Development to construct 200 

fi sh ponds in 140 constituencies 

by June 2013. According to 

existing plans, each constituency is 

geared to receive 8 million Kenya 

shillings (EUR 70,000) for ponds. 

In Kenya, the Sagana Fish farm, 

under the Fisheries Department, 

provides fi ngerlings for warm 

water freshwater species. So far, 

the centre has been effi cient in 

provision of seed fi sh to farmers 

and in research and production 

of suitable feed. Despite these 

advances, considerable investment 

is still needed to ensure the 

provision of suitable species for 

1 National Museums of Kenya, P.O. Box 40658 Nairobi, 00100, Kenya 

2 Département Biologie Intégrative, CNRS UMR 5554, Université de Montpellier II CC 63 Place Eugène Bataillon F- 34095 Montpellier Cedex 5, France 

3 Institut de Recherche pour le Développement, 213 rue La Fayette 75180 Paris Cedex 10, France

the various regions, ensuring 

development of the industry. 

With the government supporting 

new initiatives, the greatest 

challenge is to identify a suitable 

species that will ensure high 

yield, while also safeguarding 

native species from the impacts of 

introduced aquaculture species. 

Unfortunately, in Africa the search 

for suitable species for aquaculture 

has often disregarded potential 

impacts on the native species. 

The most important culture 

species are still mainly taken 

from the wild, and populations 

are often translocated to basins 

far beyond their native range, 

potentially bringing closely related 

but formerly isolated species or 

populations into contact with 

each other. Where there has been 

inadequate research and planning, 

an introduced cultured species 

may directly compete with native 

species, or may hybridize with 

them, as noted above for O. niloticus 

when it was introduced to Lake 

Victoria. Unfortunately, O. niloticus 

has, in many cases, been the species 

of choice for aquaculture, therefore 

leading to further problems of 

competition and hybridisation. 

Oreochromis leucosticus was 

originally known from drainages 

near the border of Uganda and 

the D. R. Congo, specifi cally 

Lakes Edward, and Albert, and 

associated affl uents. However, it 

was introduced to Lake Naivasha 

in Kenya in 1957 (Harper et al. 

1990). About 150km away from 

Lake Naivasha is Lake Baringo, in 

the Kenyan Rift Valley, home to the 

endemic subspecies of Nile tilapia, 

O. niloticus baringoensis. Nyingi 

and Agnèse (2007) note that O. 

niloticus baringoensis share genetic 

characteristics of O. leucosticus, 

suggesting that O. leucosticus might 

have been introduced also to Lake 

Baringo, with some subsequent 

transfer of genetic material through 

hybridization with O. niloticus 

baringoensis. Even though impacts 

of the possible introduction of 

O. leucosticus are still unknown, 

introductions of tilapiines continue 

to be made within the region, 

either intentionally or accidentally 

through escape from culture ponds. 

Such issues are a clear indication 

of a failure of well-defi ned policies, 

or implementation of the existing 

regulations, for the management 

of natural fi sheries resources in 

Kenya. Through lack of awareness, 

and desperation to increase 

yield, fi sh farmers are breeding 

alien species of tilapia that could 

naturally hybridize in a similar 

manner – as seems to have occurred 

in Lake Baringo. Consequently, 

native species may be lost in several 

parts of eastern Africa, as already 

observed in Lake Victoria. 

As noted above, a new subspecies 

of Oreochromis was recently 

discovered from the Lake Bogoria 

Hotel spring near the Loboi swamp. 

This population was formerly 

Fish farms, such as this one in Malawi, represent an important source of food and income for people throughout Africa. 

However the traits that make species such as Oreochromis niloticus suitable for aquaculture mean that they pose a signifi cant 

threat to local species should they escape. © RANDALL BRUMMETT 


77


78 

thought to have been introduced, 

but genetic and morphological 

analysis demonstrated its 

originality (Nyingi 2007; Nyingi 

and Agnèse 2007). The main body of 

the Loboi swamp acts as a physical 

and chemical barrier between the 

warm water springs (where the 

new sub-species is found) that 

fl ow into the swamp, and the 

Loboi River, which drains from it 

to Lake Baringo. The swamp has a 

signifi cantly low dissolved oxygen 

level (around 4% saturated dissolved 

oxygen, compared to around 60% 

in the springs and groundwater 

discharges), which is a consequence 

of high oxygen consumption during 

aerobic decomposition of detritus 

from macrophytes in the swamp 

(Ashley et al. 2004). 

The new apparent sub-species 

from the springs draining into the 

Loboi swamp offers interesting 

new possibilities for aquaculture 

development, if managed properly. 

The sub-species inhabits high 

temperatures (approximately 36°C) 

and may have developed hypoxic 

resistance mechanisms as dissolved 

oxygen levels may also be low. This 

sub-species may also have developed 

special mechanisms to regulate its 

sex-ratio, since sex determination 

is known to be infl uenced by 

high temperatures (Baroiller and 

D’Cotta 2001; Tessema et al. 2006). 

Therefore, the new sub-species 

may be a model for the study of sex 

determination in Oreochromis. 

However, the population from 

the Loboi swamp and associated 

rivers is under threat from human 

encroachment. The Loboi swamp 

itself has receded by around 60% 

over the last 30 years due to water 

abstraction for irrigation since 1970 

(Ashley et al. 2004; Owen et al. 2004). 

In addition, periodic avulsions 

have caused changes in the course 

of rivers in this region. The most 

recent was during the El Niñoinduced 

heavy rains of 1997, which 

caused changes in the courses of the 

Loboi and Sandai Rivers. The Sandai 

River now partly fl ows into Lake 

Baringo and partly to Lake Bogoria. 

...many challenges still lie 

ahead, and it will be critical 

to reinforce policy and 

management action with 

programmes of public awareness 

and education. 

Similarly, the Loboi River, which 

used to feed Lake Baringo, has 

changed its course and now fl ows 

to Lake Bogoria. These changes 

of fl ow were also due to intensive 

agricultural encroachment by 

local farmers leading to weakening 

of the river banks (Harper et 

al. 2003; Owen et al. 2004). This 

situation is not unique to the 

Loboi swamp but is common in 

almost all lakes and river systems in 

Kenya. The National Environment 

Management Authority in Kenya 

has been actively involved in 

ensuring rehabilitation of the 

Nairobi River, which had been 

greatly impacted due to solid waste 

disposal, sewage, run-off from car 

washes, and other human activities 

within the city and suburbs of 

Nairobi (Nzioka 2009). The success 

of this project is a clear indication 

that the National Environment 

Management Authority is able to 

protect hydrological systems in 

Kenya. There is, however, a need to 

replicate these successes elsewhere. 

Management of tilapia 

fi sheries 

A signifi cant challenge has existed 

where freshwater resources are 

shared by different countries. For 

example, fi sheries management 

of Lake Victoria was highly 

compromised in the early 1960s 

following independence of the 

countries bordering the lake 

(Kenya, Uganda and Tanzania), 

when they adopted different 

fi shing regulations based on the 

stocks targeted for exploitation 

(Marten 1979). These different 

regulations and priorities for 

exploitation have made it diffi cult 

to manage the lake as a complete 

ecosystem (Ntiba et al. 2001; Njiru 

et al. 2005). Ironically, this lack 

of management has contributed 

to declines in the introduced O. 

niloticus, which was previously 

responsible for the decline in the 

native sub-species (see above). 

Stock analyses for O. niloticus 

surveys of 1998 to 2000 and 2004 

to 2005 show that artisanal catches 

were dominated by immature 

fi sh, most being below the legally 

allowed total length of 30cm (Njiru 

et al. 2007). The paucity of mature 

individuals observed in commercial 

catches (Njiru et al. 2005) may 

be partly due to the increased 

numbers of introduced Nile 

perch (Lates niloticus) (Lubovich 

2009), but is also probably due 

to overexploitation. In the past, 

this overexploitation has been 

possible because of the laxity and 

weakness in enforcement of the 

Fisheries Act of 1991, which is 

highly explicit on the manner in 

which fi shing activities should be 

conducted. Signifi cant efforts are 

being made to address the challenge 

of providing a comprehensive, 

consistent set of policies and 

programs for sustainable 

management of the lake’s fi shery 

resources. For example, in March 

2007, Kenya, Tanzania, and Uganda 

adopted a Regional Plan of Action 

for the Management of Fishing 

Activity; this plan called on the 

respective governments to review 

their national policies and develop 

a harmonized fi shing framework 

(LVFO 2007; Lubovich 2009). 

Nevertheless, many challenges still 

lie ahead, and it will be critical to 

reinforce policy and management 

action with programmes of public 

awareness and education.


Forest remnants in western Africa – 

vanishing islands of sylvan fi shes 

A 

signifi cant part of western 

Africa is covered by 

differing types of savanna 

that are drained by a few 

large rivers, like the Niger, Volta 

and the Senegal. The vegetation 

refl ects climatic conditions 

including a cycle of dry and wet 

seasons. Closer to the coast, partly 

bordered by the Guinean highlands 

(from the highlands of the southern 

Fouta Djallon in south-eastern 

Guinea, through northern Sierra 

Leone and Liberia, to northwestern 

Côte d’Ivoire), the climate 

is more humid, allowing different 

types of forest to grow. These 

forests are inhabited by animals 

closely resembling or even identical 

to those of the central African 

forests. Thus, many sylvan (forest 

dwelling) fi sh species and speciesgroups 

fi nd their most westerly 

distributions within the western 

Africa coastal forests. A number of 

these westerly sub-populations may 

be discrete sub-species, or separate 

species within species complexes, 

showing distinct colour morphs, or 

other unique features. 

The high number of unconnected 

coastal rivers in western Africa is 

thought to have promoted these 

speciation processes, which have 

led to noticeably high levels of 

endemism, such as for characids, 

barbs and cichlids. Furthermore, 

several remarkable fi shes, which 

are sometimes called ‘relict‘ species, 

occur in the Guinean regions. 

These species belong to phyletically 

old groups previously represented 

by more numerous and widespread 

species but, following evolutionary 

events, now represented by only 

a few, often locally restricted 

species. Examples include the 

fourspine leaffi sh (Afrononandus 

sheljuzhkoi) and the African leaffi sh 

(Polycentropsis abbreviata), with 

their closest relatives in Asia and 

South America, and the enigmatic 

denticle herring (Denticeps 

clupeoides), which is the only 

extant representative of the family 

Denticipetidae, the sister group of 

all other clupeomorphs. 

The climatic conditions of the 

Guinean region not only provide 

good conditions for forest 

ecosystems, but also support a more 

diverse and reliable agriculture 

compared with the Sahelo-Sudan 

region. This promotes better 

livelihood opportunities which, in 

turn, lead to increased population 

densities and a greater demand for 

land. With increased demands for 

agricultural land, deforestation 

continues, leaving only forest 

fragments in some areas. 

1 Deutsches Meeresmuseum, Museum für Meereskunde und Fischerei – Aquarium, Stralsund, Germany 

Moritz, T. ¹ 

Lokoli swamp forest in southern Benin. This small forest fragment serves as one of 

the last refuges for many forest dwelling species. © T. MORITZ 

Lokoli forest – a refuge 

An exemplary forest remnant 

is the Lokoli swamp forest in 

southern Benin. This small, 

(approximately 500ha) piece of 

forest is permanently fl ooded by a 

network of channels from the Hlan 

River, an affl uent of the Ouémé 

River. It is approximately 20km 

east of Bohicon and 100km north 

of Cotonou and can only be crossed 

by boat. The forest is densely 

vegetated with high tree density, 

and the tree cover is usually closed 

above the channels. Most channels 

are less than a metre wide and are 

only navigable using small dugout 

canoes. Water depth varies by less 

than one metre within a year, and is 

usually around 1 to 2.5 metres. The 

water has a dark brown colouration 

due to leaf litter decomposition, a 

moderate acidic pH of 6 to 7 and a 

temperature of around 26°C. The 

channel substrate is predominantly 


79


80 

Barboides britzi, one of Africa’s smallest freshwater fi sh, is a newly described species endemic to Lokoli forest in Benin. 

© T. MORITZ 

sand, with small patches of gravel 

where the current is stronger; most 

places have a mud and leaf litter 

layer of variable depth. 

The Lokoli forest serves as one of 

the last refuges for forest dwelling 

animals in the Dahomey Gap, 

including pangolins, fl ying squirrels 

and the red-bellied monkey 

(Cercopithecus erythrogaster), 

which is endemic to Benin. While 

herpetological surveys have shown 

relatively few exclusive forest 

species of reptiles and amphibians 

(Rödel et al. 2007; Ullenbruch et 

al. 2010), the situation for fi shes 

is very different. Despite a direct 

connection to the main channel 

of the Ouémé River, fi shes of the 

Lokoli are, to a high degree, typical 

forest species, otherwise known 

from the coastal forested rivers of 

the Niger Delta and the connected 

network of lagoons parallel to the 

coast. The reedfi sh (Erpetoichthys 

calabaricus), butterfl y fi sh (Pantodon 

buchholzi), and elephant nose fi sh 

(Gnathonemus petersii) in Lokoli 

are at the most western points of 

their ranges (Montchowui et al. 

2007; pers. obs.). The cyprinid genus 

Barboides, consisting of two of the 

smallest African freshwater species, 

is also at the most westerly point 

of its range, with B. britzi endemic 

to the Lokoli forest itself. This 

miniature fi sh becomes sexually 

mature at a smaller size than any 

other freshwater fi sh in Africa, at 

12.6mm standard length (Conway 

and Moritz 2006). It is likely that 

more fi sh species, especially of 

smaller body size, await discovery 

in such unusual habitats. For 

example, the bottom dwelling 

distichodontid Nannocharax signifer 

was only recently described, from a 

small affl uent of the Lokoli forest 

(Moritz 2009). 

Impacts to this small forest 

fragment are signifi cant, with 

extensive clearance for agriculture 

along the forest margins. Within 

the forest itself, despite religious 

taboos prescribing at least some 

regulations for hunting, the bush 

meat trade remains an important 

source of income and bush meat 

is openly sold along the main road 

leading to Cotonou. Palm wine and 

secondary products are produced 

by cutting off the tops of the 

palm Raphia hookeri, with evident 

impacts to the plants themselves. 

As a result, the abundance of this 

formerly dominant palm has been 

signifi cantly reduced through 

over-harvesting. The forest fl ora 

has been further impacted through 

introduction of alien species such 

as the taro (Colocasia esculenta), an 

introduced plant valued for its root 

tubers, which is widely planted, 

even within clearings in the swamp 

forest. 

Forested coastal rivers, although 

more spacious than some of the 

Guinean forested rivers, face similar 

threats. In addition to pollution, 

which is heavily impacting certain 

areas, the primary problem is, once 

more, habitat degradation due to 

expanding agriculture. The Iguidi 

River at the border of Benin and 

Nigeria provides a good example. 

The course of this small coastal 

river is clearly visible on aerial or

satellite images, due to its bordering 

gallery forest. The forest stands out 

in stark contrast to neighbouring, 

and continuously expanding, fi elds. 

The Iguidi River fl ows in a northsouth 

direction, starting out as a 

small forested stream that develops 

into a swamp. As is typical for a 

forest stream, the water is brown to 

dark brown in colour, although the 

pH is not especially acidic, at 6.5 to 

7.5; water temperature is commonly 

26 to 29°C; and conductivity is 

low at 50 to 65µS (Moritz 2010). 

Despite the river’s low salt content, 

fi shes characteristic of brackish 

environments are also present, 

such as the freshwater pipefi sh of 

the genus Enneacampus, and the 

sleeper goby (Eleotris daganensis). 

The majority of fi shes from the 

Iguidi are, however, typically 

freshwater, forest-dwelling 

species such as the dotted catfi sh 

(Parauchenoglanis monkei), the 

small distichodontid, Neolebias 

ansorgii, and the cryptic mormyrid 

(Isichthys henryi). This small river 

represents an outpost of the Lower 

Guinean forest, and holds the most 

westerly distributions of several 

Lower Guinean species, such as the 

aforementioned Neolebias ansorgii, 

the Niger tetra (Arnoldichthys 

spilopterus), and the catfi sh 

Schilbe brevianalis (Moritz 2010). 

Furthermore, the Iguidi River is the 

type locality for the rare, miniature 

Barbus sylvaticus, the even smaller 

Barboides gracilis, and the denticle 

herring (Denticeps clupeoides), all of 

which are assessed as Vulnerable or 

Endangered. 

In conclusion, at fi rst glance, 

small forest fragments seem to 

be of minor importance for the 

conservation of forest dwelling 

species – often being too small 

to sustain endemic species, or 

even too small to harbour a 

discrete population of a sylvan 

species. Many inhabitants of 

forest remnants are, therefore, 

non-specialist or even savanna 

species. A closer view of the fi shes, 

however, reveals a quite different 

picture. Forest remnants, such as 

the Lokoli, can sustain a number 

of small endemic species. What 

is more important, however, is 

the complexity of biodiversity 

that is found and that needs to be 

conserved. Forest fragments and 

remnants of gallery forests are focal 

points of habitat complexity, edge 

effects and ecological interactions 

– and as outposts for species 

distributions, they may be of high 

importance for maintaining genetic 

variability within a species and in 

ongoing evolutionary processes. 

Therefore, despite their small size, 

forest fragments deserve greater 

focus within conservation plans; 

their inclusion will help to ensure 

preservation of biodiversity in all 

its forms. 

The freshwater butterfl yfi sh, Pantodon buchholzi (LC), a widespread species in 

Africa, reaches the most westerly point of its range in Lokoli forest, Benin. This 

species is capable of jumping out of the water to search for insects or to escape 

from predators. It is not a glider, but a ballistic jumper, with tremendous jumping 

power. © T. MORITZ 


81


82 


A unique species fl ock in Lake Tana – 

the Labeobarbus complex 

Lake Tana, in Ethiopia, and 

the rivers that drain into 

it, are home to a unique, 

endemic species fl ock 

belonging to the cyprinid genus 

Labeobarbus. The lake, which has 

a surface area of 3,150km 2 , is the 

largest in Ethiopia. It is situated 

in the north-western highlands 

at an altitude of approximately 

1,800m. It was formed during the 

early Pleistocene when a 50kmlong 

basalt fl ow blocked the course 

of the Blue Nile near its source 

(Mohr 1962; Chorowicz et al. 1998). 

Today, several rivers drain into 

Lake Tana, which itself forms the 

headwaters of the Blue Nile – the 

only river fl owing out of the lake, 

contributing more than 80% of the 

total volume of the Nile River at 

Khartoum, Sudan. 

The wetlands and fl oodplains that 

surround most of the lake form the 

largest wetland area in Ethiopia and 

are an integral part of the complex 

Tana ecosystem. The wetlands to 

the east of the lake serve as breeding 

grounds for Oreochromis niloticus 

(Nile tilapia) and Clarias gariepinus 

(North African catfi sh), both of 

which are important for the lake 

fi sheries (Vijverberg et al. 2009). 

There are 28 species of fi sh in 

Lake Tana, of which 20 are endemic 

to the lake and its catchments 

(Vijverberg et al. 2009). The fi sh 

fauna includes representatives of 

the genera Oreochromis, Clarias, 

Labeobarbus (i.e., the ‘large African 

barbs’), Barbus (i.e., the ‘small Barbus 

group’; see De Weirdt and Teugels 

2007), Garra, Varicorhinus and 

Nemacheilus. The population of O. 

niloticus in Lake Tana was described 

as a separate sub-species, Oreochromis 

1 Department of Biology, Addis Ababa University, Ethiopia 

niloticus tana. Two exotic species, 

Gambusia holbrooki and Esox lucius, 

were reported to have been brought 

from Italy during the late 1930s and 

introduced into the lake (Tedla and 

Meskel 1981); there is, however, no 

trace of these fi shes from the lake in 

recent times. 

The Labeobarbus species fl ock 

The Cyprinidae are the most 

species-rich family in the lake, 

represented by four genera, Barbus, 

Garra, Labeobarbus and Varicorhinus. 

Within the Labeobarbus is a unique 

complex of 17 species (Getahun 

and Dejen in prep.). It is thought 

that the lake is able to support such 

a large number of closely related 

species because, when it fi rst formed, 

it offered several new habitats 

that may have promoted adaptive 

radiation among the original 

colonising species, and it has since 

remained isolated due to the Tissisat 

Falls, located 30km downstream 

from the outfl ow of the lake. Most 

interesting is the speed of evolution 

for so many new species, as historical 

evidence suggests the lake dried 

out completely as recently as 16,000 

Getahun, A.¹ 

Labeobarbus macrophtalmus is a benthopelagic species that forms an important 

component of the Lake Tana fi shery. © LEO NAGELKERKE 

years ago (Lamb et al. 2007), meaning 

the evolution of the Labeobarbus 

species complex may have taken 

fewer than 15,000 years (Vijverberg 

et al. 2009). 

Eight of the Labeobarbus species 

are piscivores, and most of them 

periodically migrate into the rivers 

for spawning. L. intermedius and L. 

tsanensis are abundant in the inshore 

habitats and are the predominant 

species at the river mouths. L. 

tsanensis and L. brevicephalus are the 

dominant species offshore. 

Spawning behaviour 

Limited surveys around Lake Tana 

indicate that the Ribb, Megech and 

Dirma Rivers and their tributaries 

provide ideal breeding grounds 

for these species in the northern 

and eastern parts of the lake. Five 

species were found to migrate from 

Lake Tana up both the Megech and 

Dirma rivers to spawn (Anteneh 

2005), although slightly greater 

numbers migrate up the Megech, 

which has more tributaries with 

gravel beds, and a slightly higher 

dissolved oxygen content. Three 

categories of spawning behaviour are

observed (Anteneh 2005), obligate 

river spawners, lake spawners and 

generalists (spawning in both the 

lake and its tributary rivers). 

At least seven species spawn in 

the headwaters of the main rivers 

draining to the lake. As yet, there is 

no evidence of river-specifi city, but 

this cannot be discounted. After a 

brief pre-spawning aggregation at 

the river mouths, the adults migrate 

upstream in July and August, at 

the onset of the rainy season. Final 

maturation and spawning occur in 

the tributaries of the major rivers, or 

possibly in gravel reaches in the main 

channels. After spawning, the adults 

return to the lake for feeding until 

the next cycle of breeding. Highly 

oxygenated water and gravel beds are 

important for development of the 

eggs and larvae. Deposition of eggs 

in gravel beds prevents them from 

being washed away, and clear water 

is required to ensure they are free of 

sediments that might obstruct the 

diffusion of oxygen. 

The juveniles start to return to 

the lake in September and October 

as fl ows reduce, where they feed 

and grow to sexual maturity. There 

is good evidence that, during their 

return to the lake, the juveniles may 

remain in the pools of the main river 

segments for an extended period, 

probably until the next rainy season, 

at which time they will be carried 

into the lake. 

The lake fi sheries 

The lake fi shery is clearly very 

important to the local population, 

employing more than 3,000 people 

in fi shing, marketing, and processing 

(Anteneh 2005). Traditionally, the 

main fi shery has been a subsistence 

reed boat fi shery targeting a range 

of species, sometimes including 

the Labeobarbus species. This was 

conducted throughout the lake 

until the 1980s; since then it has 

been replaced in many areas by 

other methods. The fi shery remains 

important in the more remote areas 

of the lake, with the catch being 

sold at small markets or used for 

household consumption. It mainly 

employs gillnets, and the main target 

species is Nile tilapia (O. niloticus). 

However, the reed boat (tankwa) 

fi shermen also use hooks and lines, 

and traps, as well as spears to catch 

catfi sh. 

In 1986, motorised boats and 

nylon gill nets were introduced 

as part of the Lake Tana Fisheries 

Resource Development Program 

(LTFRDP) (Anteneh 2005). Data 

collected from all commercial 

fi sheries recognizes only four 

species groups: Labeobarbus spp., 

African catfi sh (C. gariepinus), 

Nile tilapia (O. niloticus) and beso 

(Varocorhinus beso). This fi shery 

mainly supplies larger markets, 

using 100m long gillnets. There are 

around 25 motorised fi shing boats, 

most of which land their catch in 

Bahir Dar, the main town on the 

shore of Lake Tana. The fi shery 

is, however, expanding to all 10 

Woredas (districts) bordering the 

lake, including the Gorgora area (on 

the northern shore). 

Total annual catches increased 

from 39 tonnes in 1987 to 360 tonnes 

in 1997 (Wudneh 1998). However, 

the catch per unit effort for the 

commercial gill net fi shery targeting 

Labeobarbus species dropped by 

more than 50% over the period 

1991 to 2001 (de Graff et al. 2004). 

The same authors have reported a 

75% decline (in biomass) and 80% 

(in number) of landed fi sh of the 

species of Labeobarbus (L. acutirostris, 

L. brevicephalus, L. intermedius, L. 

macrophthalmus, L. platydorsus and 

L. tsanensis) in the southern gulf 

of Lake Tana. The most plausible 

explanation for the decline is 

recruitment overfi shing by the 

commercial gillnet fi shery (de Graff 

et al. 2004), and poisoning of the 

spawning stock in rivers using the 

crushed seeds of ‘birbira’ (Milletia 

ferruginea) (Nagelkerke and Sibbing 

1996; Ameha 2004). 

The commercial gill net fi shery 

for species of Labeobarbus is 

highly seasonal and mainly targets 

spawning aggregations, as more 

than 50% of the annual catch is 

obtained in the river mouths during 

August and September. There is 

also a chase and trap fi shery based 

in the southern part of the lake, and 

longlines, cast nets and traps are 

occasionally used but contribute 

little to the total fi sh catch. 

Threats to Lake Tana and its 

Labeobarbus species 

Overfi shing 

Although a fi shery policy has been 

developed both at federal and 

regional levels, it is not effectively 

Fishermen cast their lines from papyrus boats ("tankwas") on Lake Tana in northern 

Ethiopia. Behind them lies the source of the Blue Nile. Near Bahir Dar, Ethiopia. 

© A. DAVEY 


83


84 

implemented. Lakes and rivers 

are, unoffi cially, considered to be 

resources that are freely available 

to everyone. There are still many 

illegal, unregistered fi shermen 

exploiting the fi sh resources, and 

there is little regulation of fi shing 

gears. As reported above, this has 

led to overfi shing of Labeobarbus in 

some parts of the lake, especially in 

the south around the town of 

Bahir Dar. 

Habitat disturbance 

As seasonal fl ooding recedes, many 

people use the shores of the lake for 

‘fl oodplain recession agriculture’. 

Human encroachment on the 

wetlands increases every year, 

with the subsequent depletion of 

emergent macrophytes through 

harvesting and burning, while 

there is an expansion of submerged 

macrophyte stands in other areas. 

Over the last 15 years, 

deforestation has become very 

widespread, facilitating conditions 

for soil erosion, resulting in 

sediments draining into the lake 

and smothering upstream spawning 

areas. The soil loss rate from areas 

around the lake is between 31 and 50 

tonnes per hectare per year (Teshale 

et al. 2001; Teshale 2003). These 

huge deposits of sediment into the 

lake have led to a reduction in the 

lake’s area, a drop in water levels, 

and a loss of water holding capacity. 

This reduction in the water level 

has resulted in fragmentation of the 

available aquatic habitat, especially 

around shores. Some of the exposed 

land is now used for cultivation and 

excavation of sand. 

Water pollution 

Run-off from small-scale agriculture 

around the lake is bringing 

agricultural fertilizers, pesticides 

(including DDT), and herbicides 

into the lake. The use of these 

agricultural products by farmers 

is still relatively limited; however, 

a lack of effective regulation on 

their use presents a potential threat 

to water quality in the lake. Other 

chemicals, such as ‘birbira’ (Milletia 

Many of the Labeobarbus species migrate up the rivers fl owing into Lake Tana to 

spawn in gravel beds, such as seen here in the Gumara River. © LEO NAGELKERKE 

ferruginia) seed powder (used as an 

ichthyocide; see above), may also 

pollute the lake and kill the aquatic 

fauna, including Labeobarbus species. 

Domestic waste water from the 

town of Bahir Dar is, in most cases, 

discharged directly into Lake Tana – 

the development of an appropriate 

sewage system could solve or 

mitigate these pollution threats. 

Water abstraction and 

impoundment 

Water abstraction occurs at some 

points around the lake as a result of 

privately run, small-scale irrigation 

projects. However, because the 

Lake Tana and Beles sub-catchment 

is considered a growth corridor 

by the federal and regional 

governments, there are several other 

dam and irrigation projects under 

consideration or being implemented. 

These include the Tana Beles interbasin 

water transfer project, and the 

Koga, Ribb, Megech, Gilgel Abay 

and Gumara dams and irrigation 

projects. Some of these are intended 

to impound the lake’s tributaries to 

store water; some to pump water 

through tunnels from the lake 

to a hydropower facility before 

discharging the water into the Beles 

River; and some to pump water 

directly from the lake for irrigation 

purposes. These projects may lower 

the water level and quality in Lake 

Tana and its tributaries, with 

subsequent impacts to biodiversity. 

As reported above, many species 

of Labeobarbus undergo spawning 

migrations that, without effective 

measures to allow passage past 

newly constructed dams, may be 

blocked, potentially leading to the 

extinction of this unique fl ock of 

cyprinids. Environmental impact 

assessment (EIA) studies have 

been conducted for many of these 

projects, so it is hoped that the 

recommended mitigation measures 

and the management plans 

suggested will be strictly followed 

and implemented. 

Lack of information and 

institutional capacity 

Comprehensive scientifi c studies 

on the biology, behaviour, and 

ecology of the different species of 

Labeobarbus are still lacking. This 

makes it diffi cult to recommend 

mitigation measures in some of 

the EIA studies and follow up 

with implementation. In addition, 

the implementing agencies for 

EIAs still lack the strength and 

capacity to enforce and implement 

any recommendations made. The 

development of a Lake Tana subbasin 

authority is an option for 

solving this problem. Concerted 

action by all stakeholders is 

required if the unique fi sh fauna of 

this lake is to be conserved for the 

future.

The Twee redfi n, Barbus 

erubescens, a Critically Endangered 

fi sh from the Twee River, South 

Africa, where it is threatened by 

alien fi sh species. © D. IMPSON 


The Twee River redfi n – a Critically 

Endangered minnow from South Africa 

The Twee River redfi n 

(Barbus erubescens Skelton) 

was described in 1974, 

following an investigation 

that included extensive fi eld 

observations. The species is named 

for the bright reddish breeding 

dress assumed by spawning 

males, with females being less 

intensely coloured. The common 

name indicates that the species’ 

distribution is restricted to one 

tributary system of the Olifants 

River in the Cedarberg Mountains 

of the Western Cape, South Africa. 

This tributary system includes the 

Twee and some of its affl uents, the 

Heks, Suurvlei and Middeldeur 

rivers. 

At the time of discovery, only 

one other fi sh species was known 

to be indigenous to the Twee River, 

and both species were isolated by 

a vertical waterfall of about 10m, 

located close to the confl uence 

of the Twee and Leeu rivers. This 

other indigenous fi sh is a species of 

South African Galaxias, formerly 

named as the Cape galaxias 

(Galaxias zebratus); however, more 

recently it has become evident 

that a number of populations of G. 

zebratus might represent distinct 

species. The population of Galaxias 

1 South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa 

Skelton, P.H.¹ 

in the Twee River is one of these 

distinct populations. The Cape 

galaxias is currently assessed in the 

IUCN Red List as Data Defi cient, 

due to the taxonomic confusion 

associated with the species 

complex. Below the falls several 

other indigenous freshwater fi sh 

species are found, most of them 

endemic to the Olifants system. 

One of these species, Barbus calidus, 

is the sister species of B. erubescens 

(i.e., it is the phylogenetically 

most closely related species to 

B. erubescens). Barbus calidus, the 

Clanwilliam redfi n, itself classifi ed 

as Vulnerable, due to threats 


85


86 

from invasive species, and habitat 

degradation caused by agriculture, 

is discussed below. 

Much has been learnt about the 

Twee River redfi n since its original 

description. In common with a 

disproportionately large number 

(80%) of barbine minnows from 

the temperate reaches of southern 

Africa, the Twee River redfi n is 

tetraploid (that is, it has four sets 

of each chromosome), with 100 

chromosomes in total. Its most 

distinctive external character is 

the high number of branched anal 

fi n branched rays – six or, more 

usually, seven – more than any 

other African barbine species. It has 

several other distinctive features, 

such as small scattered nuptial 

tubercles on both sexes, two pairs 

of well developed mouth barbels, 

and an unbranched ray in the dorsal 

fi n that shows either incipient or 

vestigial serrations. 

The species’ breeding behaviour 

features males congregating and 

forming a dense, swarming, nuptial 

school against rock surfaces to 

which individual breeding females 

are attracted and enticed to spawn 

over cobbles or rock crevices with 

several pursuant males. This occurs 

in spring or early summer (October 

to December) when streams are 

swollen by frontal rains. The 

species is a ‘broadcast spawner’ 

(releasing the gametes into the 

water) and does not practice any 

form of parental care. It can live for 

up to fi ve or six years. The species 

feeds on drifting insects and other 

invertebrates or from rocks and 

other benthic surfaces. 

Conservation concerns 

When fi rst discovered, the species 

was common and widespread in 

the tributary system – with larger 

adults occupying open water 

habitats in pools and runs, and 

juveniles shoaling along marginal 

zones. Since the 1970s, the 

population has declined markedly 

and is absent from large sections of 

its former range. The reasons for 

this decline are several, including 

The Twee River in the Cedarburg Mountains, the Western Cape, South Africa. 

© SAIAB/P. SKELTON 

likely impacts from agricultural 

developments (riparian fruit 

orchards) impacting both water 

quality and quantity, and alien 

invasive fi sh species. The fi rst 

alien fi sh species to be recorded 

was a South African anabantid, 

the Cape kurper (Sandelia capensis) 

which, although not a large fi sh, 

is widespread throughout most 

of the tributary and an avid 

predator on small fi shes and 

invertebrates. The Clanwilliam 

yellowfi sh (Labeobarbus capensis), 

a large cyprinid of the Olifants 

River system, was introduced to 

the Twee River above the barrier 

waterfall by Nature Conservation 

authorities seeking to conserve 

that species in the face of threats 

from other introduced species! The 

Clanwilliam yellowfi sh is found 

mainly in the downstream reaches 

of the Twee and, although its 

precise impact is not known, it is 

a predator and grows much larger 

that the Twee River redfi n. Bluegill 

sunfi sh (Lepomis macrochirus), 

a North American centrarchid 

species, and another predator on 

small fi shes and invertebrates, have 

also invaded the system. Rainbow 

trout (Oncorhynchus mykiss) have 

been recorded from the Twee River 

but are not common. 

The Twee River has been 

extensively surveyed on several 

occasions to determine the 

conservation status of the redfi n 

and the Galaxias species. The 

decline in their populations is of 

great concern, as the tributary 

system is restricted in size and 

subject to increasing agricultural 

pressures as well as the invading 

alien species. There are few natural 

sanctuary reaches and, unless 

determined action to remove the 

alien species is taken, the fate of 

the threatened indigenous species 

might be sealed forever. Two things 

are essential for conservation 

action – political will by the 

authorities to do what they must 

in the face of contrary perceptions 

by the public (who, for example, 

may support introductions of 

species for fi shing), and a properly 

informed public, especially the 

local landowning public. If those 

elements are in place, the survival 

of these and other indigenous 

species in South Africa might 

be secured.


Cauldrons for fi sh biodiversity: 

western Africa’s crater lakes 

Globally, crater lakes 

are comparatively 

rare, usually small and 

specialised freshwater 

habitats formed in geological 

depressions, such as the Ojos del 

Salado in the Andes mountains, 

bordering Argentina and Chile 

– probably the highest altitude 

permanent lake of any description 

(68º32′W, 27º07’S, elevation 6,390m, 

diameter 100m, depth perhaps 

5 to 10m). Crater lakes are well 

represented in tropical Africa, 

especially in the Guinean rainforest 

zone of Cameroon, where there 

may be 36 or more. The entire 

region is a celebrated ‘biodiversity 

hotspot’ for both lacustrine and 

riverine fi shes (Reid 1989; 1996; 

Teugels et al. 1992; Schliewen 2005; 

Stiassny et al. 2007). Contemporary 

general studies on the world’s 

crater lakes address important 

topics such as: lake formation; 

physical, chemical, geological, 

geographical and biological 

evolution; paleoecology; historical 

biotic colonisation; and recent 

ecology – including the assessment 

of conservation status and threats 

to the survival of the contained 

habitats and species. The potential 

for (and impacts from) human use 

is studied, including water supply, 

agriculture, fi sheries and also 

recreation and ecotourism – such 

lakes often being scenic locations. 

Crater lakes everywhere may 

contain a substantial number 

of endemic fi shes and other 

aquatic and amphibious taxa. 

Among African fi shes endemic to 

craters, small phyletic and trophic 

assemblages of species and genera 

representing the family Cichlidae 

have attracted much international 

scientifi c attention. Crater lake 

cichlids, their taxonomy, phylogeny 

and ecology were documented early 

on in Cameroon, notably in Lake 

Barombi Mbo (Trewavas 1962; 

Trewavas et al. 1972; see below); and 

they continue to be discovered – for 

example, the recently documented 

‘fl ock’ of eight new species of Tilapia 

from Lake Bermin or Beme (5°9’N, 

9°38’E; diameter around 700m, depth 

around 16m, and age probably far 

less than 1 million years) (Stiassny 

et al. 2002; Schliewen 2005). Such 

Cameroonian assemblages are often 

regarded as small-scale tilapiine 

counterparts to the better known 

large haplochromine and other 

cichlid ‘species fl ocks’ of the East 

African Great Lakes (Klett and 

Meyer 2002; Salzburger and Meyer 

2004). 

Formation 

Whatever the location, all craters 

on earth are formed either by 

impact of extraterrestrial bodies or 

1 North of England Zoological Society, Caughall Road, Upton, Chester CH2 1LH, UK 

McGregor Reid, G.¹ and Gibson, C.¹ 

Stomatepia mongo, a Critically Endangered cichlid endemic to Lake Brombi Mbo, 

Cameroon. © OLIVER LUCANUS/BELOWWATER.COM 

by vulcanism (Decker and Decker 

1997; Sigurösson 1999). They are 

often visible in photographic, radar 

and other imagery taken from space 

(Hamilton 2001). 

Impact crater lakes 

The impact of a meteorite, asteroid 

or comet creates a depression. This 

can be a simple bowl (depth to 

diameter ratio typically 1:5 to 1:7) 

or a larger, shallower, more complex 

depression (depth to diameter 

ratio 1:10 to 1:20) sometimes 

incorporating a central island or 

islands. Such islands are caused 

by a gravitational collapse of the 

rim and a rebound of material 

to the centre, analogous to the 

splash effect seen when raindrops 

hit water. An island may itself 

incorporate a hollow that later 

forms a ’lake within a lake’, as in 

Lake Taal, Philippines (Reid pers. 

obs.). In geological terms, impact 

depressions occur frequently but 

are often temporary, and only 

some 120 are currently known 


87


88 

Lake Barombi Mbo, Cameroon. This lake is considered to be the oldest radiocarbon-dated crater lake in Africa. © U. SCHLIEWEN 

worldwide, most commonly 

from North America, Europe 

and Australia. Their occasional 

occurrence in Africa is therefore of 

considerable scientifi c interest. It is 

postulated that multiple terrestrial 

impacts, particularly large ones, are 

of importance in both geological 

and biological terms and are likely 

associated with periodic species 

extinction events on land and in 

the marine environment occurring 

since at least the Cretaceous period 

(around 60 million years ago). The 

nature, persistence and effects 

of impact depressions depend on 

the ‘target’ substrate, the velocity 

of the impactor, its composition 

and identifying ‘signature’ – the 

physical and chemical outputs, 

such as meteorite shards, shock 

metamorphism, ‘rock melt’ and 

silica rich glasses. All of this may 

become biotically signifi cant at 

some later stage of lake evolution. 

Other factors determining 

nature and persistence include 

the location, scale and form of 

the depression, and subsequent 

chemical, geological, geographical 

and biological processes including 

any underlying volcanic activity, 

erosion, deposition of sediments 

and ecological colonisation. 

Aorounga, in the Sahara Desert 

of northern Chad, contains a rare 

western Africa example of a large, 

ancient, much eroded impact 

crater (19°6’N, 19°15’E; diameter 

17km; age around 200 million 

years ago (Hamilton 2001)) which 

supports isolated temporary 

pools in rainy periods. Across the 

Sahelian region such pools may 

contain a remarkable density 

of life, albeit briefl y, including 

anacostracan crustaceans (‘fairy 

shrimps’) emerging from eggs 

resting in the sand since previous 

inundations of water; and anuran 

(frog and toad) tadpoles which 

appear ‘as if from nowhere’ (Reid 

pers. obs.). However, the craters 

are usually dry and contribute a 

fi ne diatomaceous lake substrate 

to dust storms generated within 

the Bodélé Depression and which, 

in winter, amount to an average of 

1,200,000 tonnes of dust per day 

carried for hundreds or thousands 

of kilometres (Todd et al. 2007). 

The Arounga crater is one of a local 

series, which may have been part 

of the more permanent and far 

more extensive ‘Mega Lake Chad’ 

dating from the Pleistocene to 

Holocene periods (around 2 million 

years ago to 10,000 years ago) and 

persisting to some extent until a 

few thousand years ago. Lake Chad 

is now only 5% of its volume in 

the 1960s, mainly due to excessive 

human abstraction demands. The 

Mega Chad has been crucial in 

determining much of the large-scale 

aquatic and terrestrial patterns in 

historical and recent biogeography 

for western Africa and the Nilo- 

Sudan ichthyological province 

(Reid 1996). 

Lake Bosumtwi, Ghana is a better 

known, but still scarce, example of 

a comparatively young, permanent 

impact crater lake (06°32’ N, 

01°25’W; rim diameter 10.5km; 

maximum depth 75m; age 1.3 ± 0.2 

million years). The largest single 

natural lake in sub-Saharan western 

Africa, it lies over crystalline 

bedrock of the West African 

Shield and research indicates that 

sediments associated with Lake 

Bosumtwi have spread to the Ivory 

Coast and to oceanic deposits, 

nearby in the Gulf of Guinea 

(Hamilton 2001; Embassy of the 

Federal Republic of Germany 2011). 

Volcanic crater lakes. 

Craters formed through vulcanism, 

and their associated lakes, are 

sometimes divided into two 

classes: calderas which are deep 

inverted cones; and maars which 

are shallower with a low profi le. 

However, these distinctions are 

not always obvious, and the nature 

of the volcanic activity can be 

complex (Decker and Decker 

1997). The rocky rim is often 

created in a gaseous explosion 

when hot volcanic lava or magma 

in a subterranean chamber makes 

contact with groundwater.

By contrast, Lake Barombi 

Mbo is small (see above) and 

estimated to be biologically 

mature since about 25,000 to 

33,000 years ago; it is considered 

to be the oldest radiocarbondated 

crater lake in Africa 

Subsidence of materials creates a 

depression within the rim that may 

later fi ll with water. A diatreme 

often persists under the lake bed, 

that is, a pipe-like vertical volcanic 

vent that is fi lled with broken and 

cemented rock created by a single 

explosion. Such diatremes may 

remain active. Lake Nyos (around 

322km north-west of Yaoundé, 

Cameroon, close to the border with 

Nigeria) is an example of a simple 

maar lake, but a comparatively 

deep one (6°26′17″N, 010°17′56″E; 

1,091m above sea level; 2km long by 

1.2km wide; and 208m maximum 

depth). Lake Barombi Mbo in 

south-west Cameroon is formed in 

a caldera, albeit a fairly small one 

(4°39’46’’N, 9°23’52’’E; 303m above 

sea level; 2.15km wide; and around 

110m maximum depth) (Schliewen 

2005; Lebamba et al. 2010). 

Lake development 

Whether formed by impact or 

vulcanism, craters that persist 

anywhere may periodically or 

permanently fi ll up with water 

from snow, rainfall, groundwater, 

a captured drainage, spring or 

swamp or a larger inundation. 

Depending on water supply, 

drainage and evaporation, the 

lake may reach the lowest point 

on the rim and then overspill as a 

waterfall if the rim is high; or as a 

stream, if at the outset the rim is 

low or becomes water eroded. At a 

critical point of attrition there can 

be catastrophic breakout fl ooding. 

If the crater contains an active 

volcanic vent (see ’diatreme‘ above) 

the water will have an elevated 

temperature and be turbid and 

acidic from high concentrations 

of dissolved volcanic gases and 

distinctly green, or red-brown if 

iron rich. Gases include carbon 

dioxide (CO 2 ), sulfur dioxide (SO 2 ), 

hydrogen chloride (HCl) and 

hydrogen fl uoride (HF), which may 

persist in solution and are lethal to 

invertebrate and vertebrate life. 

Lake Nyos, with a diatreme some 

80km below the lake bed, is one of 

only three known contemporary 

‘exploding’ and periodically lethal 

lakes, all of which are African 

(the others being nearby Lake 

Monoun, Cameroon (5°35’N, 

10°35’E) and Lake Kivu, Rwanda). 

Nyos and Monoun are located 

within the Oku Volcanic Field 

near the northern boundary of the 

Cameroon Volcanic Line, a zone 

of volcanoes, maars, calderas and 

other tectonic activity that extends 

south-west to the large, inactive 

Mount Cameroon composite 

volcano (stratovolcano) and beyond 

to the island of Bioko in the Gulf 

of Guinea, which also contains an 

unexplored crater lake (Flesness, 

pers. comm.). Nyos has periodically 

been supersaturated with carbon 

dioxide (CO 2 , forming carbonic 

acid) leaching from the underlying 

magma and with a peak lake 

density of approximately 90 million 

tonnes of CO 2 . In 1986, there 

was a gaseous explosion, perhaps 

precipitated by an earthquake or 

landslide, releasing approximately 

1.6 million tonnes of CO 2 into 

the atmosphere. This killed some 

1,800 people, 3,500 livestock, and 

gas in solution presumably killed 

fi shes and other aquatic life. 

Degassing pipes were installed 

in 2001 to prevent a repetition of 

the catastrophe (Kling et al. 2005). 

Some 2,000 times larger than Nyos, 

Lake Kivu has also been found to 

be periodically supersaturated – 

with evidence for outgassing every 


89


90 

thousand years or so. The general 

ability of crater lakes to store 

carbon dioxide at depth for long 

periods and also release it is clearly 

important when calculating lake 

stability, contemporary carbon 

sequestration and ‘footprints’ – 

and in determining the survival, 

ecology and evolution of fi shes and 

other aquatic animal populations. 

In the case of large mature 

impact craters and inactive or 

dormant volcano craters, the water 

normally becomes thermally and 

eventually ecologically stratifi ed. 

The deep, cold, dense, aphotic and 

anoxic water above the lake bed 

is usually quite separate from the 

warm, less dense, sunlit surface 

layers which support most of 

the animal and plant species and 

biomass. Lake surface waters 

down to around 40m are usually 

life supporting and fresh but 

can, in some instances, be saline. 

The clarity or transparency (and 

hence transmission of sunlight, 

level of photosynthetic activity 

and primary production) can be 

high, but this is determined by 

the nature of the crater rim soil 

and biota above the waterline 

(Elenga et al. 2004; Lebamba et al. 

2010), nutrients, water movements 

(including infl ows, outfl ows and 

overturns of thermal strata), and by 

other limnological processes. Some 

crater lakes are of considerable 

maturity and scale, for example, 

the Lake Toba caldera, Danau Toba, 

Indonesia was formed around 

70,000 years ago, with an area 

of over 1,000km². By contrast, 

Lake Barombi Mbo is small and 

estimated to be biologically mature 

since about 25,000 to 33,000 years 

ago; it is considered to be the oldest 

radiocarbon-dated crater lake in 

Africa (Elenga et al. 2004; Lebamba 

et al. 2010). The physical origin 

of the lake has been estimated 

as around 1 million years ago 

(Schliewen 2005). In any event, 

there is contemporary evidence 

that substantial permanent bodies 

of water can form very quickly in 

craters, for example, the lake that 

The craters represent a 

younger, less complex (if 

potentially more volatile) 

ecosystem – a ‘microcosm’ more 

easily studied than the East 

African Great Lakes 

developed post 1991, following 

the eruption of Mount Pinatubo, 

Philippines. 

Lake colonisation and the 

evolution of species. Western 

African and other small crater 

lakes have attracted the attention 

of evolutionary biologists and 

conservationists mainly because of 

their endemic cichlid fi shes and the 

natural and anthropogenic threats 

to their survival. The craters 

represent a younger, less complex 

(if potentially more volatile) 

ecosystem – a ‘microcosm’ more 

easily studied than the East African 

Great Lakes. Such craters provide 

an opportunity to investigate 

stages in ecological colonisation 

from an initially lifeless 

environment, and the processes 

of population differentiation 

and speciation. While invariably 

occupied by invertebrates, not 

all western African crater lakes 

contain fi shes and shrimps 

(Schliewen 2005). For those which 

contain cichlids, and which are 

geologically isolated, the question 

of how they came to occupy the 

crater is intriguing. In some cases, 

there are potentially testable 

hypotheses of natural migration 

through large-scale paleo-historical 

indundations of water, or via 

crater stream outfl ows (some still 

extant). Notions of paleo-historical 

introductions of fi shes or eggs by 

humans or birds are less credible 

and diffi cult, or impossible, to 

test scientifi cally. Setting such 

possibilities aside, western 

African models of tilapiine cichlid 

speciation or adaptive radiation are 

being tested against the classical 

grand-scale eastern African model 

(Klett and Meyer 2002; Salzburger 

and Meyer 2004; Seehausen 2006). 

Evidently, the evolution of 

species fl ocks is not invariably an 

enclosed, lacustrine phenomenon 

or confi ned to cichlid taxa. 

However, for Salzburger and 

Meyer (2004): ‘Species richness 

seems to be roughly correlated 

with the surface area, but not the 

age, of the lakes. We observe that 

the oldest lineages of a species 

fl ock of cichlids are often less 

species-rich and live in the open 

water or deepwater habitats.’ Based 

initially on Lake Victoria, the 

general eastern African hypothesis 

is that haplochromine and other 

cichlid taxa evolved into lacustrine 

species fl ocks numbering in the 

hundreds through a process of 

allopatric speciation, that is, one 

involving periodic geographical 

separation of populations. It 

was suggested that a regular rise 

and fall of waters in geological 

time created satellite lakes to 

isolate cichlid populations, which 

then differentiated ecologically, 

morphologically, behaviourally and 

genetically into distinct species. 

These isolates supposedly later 

returned to the main lake during 

high paleo-historical water levels 

,but by that time did not interbreed 

with their congeners. 

An alternative model is that 

species can arise as monophyletic 

fl ocks within the body of a lake 

without such total isolation, 

that is, through a process of 

sympatric speciation. In testing 

these competing (but not

necessarily mutually exclusive) 

models, Schliewen et al. (2001) 

conducted a ‘gene fl ow’ study 

within fi ve tilapiine morphs 

endemic to Lake Ejagham, 

western Cameroon (5°44’59”N, 

8°59’16”E; surface areas 0.49km 2 ; 

maximum depth around 18m 

(Schliewen 2005)). Comparisons 

with a closely related riverine 

outgroup of cichlids suggest that 

synapotypic colouration and 

‘differential ecological adaptations 

in combination with assortative 

mating could easily lead to 

speciation in sympatry’ (Schliewen 

et al. 2001). More generally, it 

is postulated that a dynamic 

network of gene exchange or 

hybridization among populations 

creates a process of ‘reticulate 

sympatric speciation’ among 

Cameroonian crater lake cichlids 

(Schliewen et al. 1994; Schliewen 

1996, 2005; Schliewen and Klee 

2004). Comparable empirical 

research on post-colonisation 

cichlids in a young crater lake in 

Nicaragua also supports the idea 

that sympatric endemic ‘morphs’ 

of individual cichlid species may 

diversify rapidly (say, within a 

hundred years or generations) in 

ecology, morphology and genetics 

and this can be interpreted as 

‘incipient speciation’ (Elmer et al. 

2010). Again, this is postulated to 

be through disruptive selection, 

perhaps sexual selection, mediated 

by female mate choice. 

Conservation of crater lake fi shes. 

The phylogenetic and associated 

data on crater lake cichlid species 

fl ocks (above) are at different 

levels of generality and, among 

other criteria, important in 

the evaluation of conservation 

priorities (Stiassny and de Pinna 

1994). However, a paucity of 

well-worked and wide-ranging 

studies has until recently limited 

such contributions (Stiassny 

2002; Stiassny et al. 2002). Even 

so, western African crater lakes 

are included as an important 

biogeographic category within 

standard recognised freshwater 

ecoregions of the world and Africa 

(Thieme et al. 2005; Abell et al. 

2008). 

Thieme et al. (2005) designate 

closed basins and small lakes 

as a ‘major habitat type’, whose 

ultimate conservation status within 

most of the western African block 

of ecoregions is under threat ‘based 

on projected impacts from climate 

change, planned developments, 

and human population growth’. 

Recent research on pollen, biomes, 

forest succession and climate in 

Lake Barombi Mbo crater during 

the last 33,000 years or so suggests 

the persistence of a humid, dense, 

evergreen cum semi-deciduous 

forest: ’These forests display a 

mature character until ca 2800 cal 

yr BP then become of secondary 

type during the last millennium 

probably linked to increased 

human interferences [our emphasis]’ 

(Lebamba et al. 2010). 

The recent conservation status 

of small Cameroonian crater 

lakes, including Barombi Mbo, 

and their endemic fi shes and 

invertebrates, is considered in 

detail by Reid (1989, 1990a,b, 1995, 

1996) and Schliewen (1996, 2005). 

Such unique lake environments 

and endemic species are clearly 

of national and international 

importance. There is, from the 

outset, an inherent vulnerability 

of these ecosystems resulting 

from the geological instability in 

craters; their small physical size; 

the small size of the contained 

populations and their genetic 

isolation; and, for cichlid fi shes, 

their methods of reproduction 

and limited fecundity. Actual or 

potential general threats are widely 

familiar, including: overfi shing 

and other socio-economic factors, 

including pressure from external 

visiting tourists; the introduction 

of alien species (for example, 

crustaceans and fi shes (Slootweg 

1989)); siltation and a reduction or 

loss of allochthonous food supply 

of terrestrial plant material and 

invertebrates (both resulting from 

deforestation and slash and burn 

agriculture within the crater rim); 

adverse water level fl uctuation 

(from damming the lake outfl ow 

and from excessive abstraction); 

and water pollution (from natural 

volcanic gases, from aerial and 

industrial emissions travelling 

from a distance; and from locally 

applied agrochemicals, pesticides 

and ichthyotoxic molluscicides 

used to control the aquatic snail 

vectors of human schistosomiasis, 

at least endemic in Barombi Mbo). 

Among conservation 

recommendations that have 

been proposed by the authors 

(above) are: systematic Population 

and Habitat Viability Analyses, 

as formulated by the IUCN 

Conservation Breeding Specialist 

Group; Red List threat assessments 

(as summarized in this volume); 

the formal designation of lakes as 

legally and practically protected 

aquatic nature reserves of national 

and international importance, with 

an accompanying conservation 

action plan (Lakes Barombi Mbo 

and Ejagham have now been 

designated as forest reserves 

(Schliewen 2005)); and ex situ 

programmes for the conservation 

breeding of species at risk, 

with the prospect of eventual 

reintroduction in appropriate 

circumstances (such ex situ 

aquarium breeding programmes 

have been in operation since 1999 

through European and North 

American Fish Taxon Advisory 

Groups). Despite the persistent 

threats outlined above, a survey of 

Lake Barombi Mbo in 2002 found 

all fi sh species to still be present 

(Schliewen 2005). However, 

many of the species present 

are threatened (even Critically 

Endangered), but there have been 

no recorded fi sh or invertebrate 

population declines to the point 

of extinction in any of the crater 

lakes. Nevertheless, continued 

vigilance, conservation monitoring, 

threat assessment, mitigation and 

protective measures remain highly 

appropriate. 


91

Chapter 3 Fishes - IUCN

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