The Congo blind barb: Mbanza- Ngungu's albino cave - IUCN

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 


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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.


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


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

The Congo blind barb: Mbanza- Ngungu's albino cave - IUCN

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