LIFE S C IENC ES GRO UP
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ISSN:
Research Article
Some epidemiological
aspects of Myxosporean
infections in Oreochromis
niloticus (Linnaeus, 1758) and
Hemichromis fasciatus (Peters,
1857), two cultured Cichlid
fishes in the West - Cameroon
2455-8400
DOI: https://doi.org/10.17352/ijafs
Received: 05 January, 2022
Accepted: 16 February, 2022
Published: 17 February, 2022
*Corresponding authors: Fonkwa Georges, Laboratory
of Aquaculture and Demography of Aquatic Resources,
Institute of Fisheries and Aquatic Sciences, Department
of Aquaculture, University of Douala, P.O. Box 7236
Douala, Cameroon, Tel: (+237) 674 29 89 24; E-mail:
ORCID: https://orcid.org/0000-0002-1698-5268
Copyright License: © 2022 Fonkwa G, et al. This is
an open-access article distributed under the terms
of the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original author and
source are credited.
https://www.peertechzpublications.com
Fonkwa Georges1,2*, Nack Jacques1, Kouam K Marc3,
Tomedi Eyango Minette1 and Tchoumboue Joseph2
Laboratory of Aquaculture and Demography of Aquatic Resources, Institute of Fisheries and Aquatic
1
Sciences, Department of Aquaculture, University of Douala, P.O. Box 7236 Douala, Cameroon
Applied Hydrobiology and Ichthyology Research Unit, Department of Animal Production, Faculty of
2
Agronomy and Agricultural Science, University of Dschang, P.O. Box 222, Dschang, Cameroon
Physiology and Animal Health Research Unit, Department of Animal Production, Faculty of Agronomy
3
and Agricultural Science, University of Dschang, P.O. Box 118, Dschang, Cameroon
Abstract
In order to assess epidemiological aspects of myxosporean infection in cultured Oreochromis niloticus and Hemichromis fasciatus fishes in Cameroon to develop
efficient prevention and control program, a total of 320 Cichlid fishes (189 Oreochromis niloticus and 131 Hemichromis fasciatus) were collected from June 2019 to April
2020 in the ponds located at the Ngoundoup Village, Koutaba Subdivision, Noun Division, Region of West-Cameroon. They were examined both macroscopically and
microscopically for myxosporean infections. The prevalence of infection was determined as a function of fish species, sex, size, target organs, and seasons. Results
showed that kidneys and ovaries were the only infected organs and harbored nine and three myxosporean species of the genus Myxobolus respectively. A total of 154
fish were infected (54.38%). Irrespective of the parasite species, Oreochromis niloticus (75.13%) was significantly more infected than Hemichromis fasciatus (24.27%).
The prevalence of parasites was very low (<25%) whatever the fish species. The sex and fish size did not significantly influence the prevalence of parasite species. The
prevalence of Myxobolus tilapiae was negatively and significantly correlated (r= -0.20; p= 0.02) with Oreochromis niloticus size. The overall prevalence was significantly
higher during the dry season (88.76%) than during the rainy (75.31%) and the transitional (20.29%) seasons. Oreochromis niloticus was not infected during the transitional
season while Hemichromis fasciatus was more infected (p<0.001) during the dry season (26.84%) followed by the rainy (15.80%) and the transitional (10.32%) seasons.
The high prevalence of myxosporeans infection may decrease the fish farming yield. The epidemiological data recorded help develop prevention and control strategies to
boost the production of Oreochromis niloticus and Hemichromis fasciatus in Cameroon.
Keywords: Fish; Myxosporean infections; Prevalence; Epidemiology; Cameroon
Introduction
Fish farming is an important socio-economic activity in a
rural community, contributing to livelihoods, food security, and
poverty alleviation [1]. This certainly explains why in Cameroon
rural community is paying a lot of attention to fish farming,
and investments in this sector are increasing in order to meet
the high demand for animal proteins induced by population
explosion. Many fish farms have been constructed among
which the most important are the Ngoundoup fish ponds, in
the Koutaba subdivision, Noun Division, West-Cameroon. In
these ponds, two Cichlid fishes are reared and appreciated by
households for consumption. These fishes include Oreochromis
niloticus and Hemichromis fasciatus commonly called Nile tilapia
and banded jewel fishes respectively.
001
Citation: Fonkwa G, Nack J, Kouam KM, Tomedi EM, Tchoumboue J (2022) Some epidemiological aspects of Myxosporean infections in Oreochromis niloticus
(Linnaeus, 1758) and Hemichromis fasciatus (Peters, 1857), two cultured Cichlid fishes in the West - Cameroon. Int J Aquac Fish Sci 8(1): 001-009.
DOI: https://dx.doi.org/10.17352/2455-8400.000073
https://www.peertechzpublications.com/journals/international-journal-of-aquaculture-and-fishery-sciences
Having the full mastery of farming skills is not the
sole prerequisite for success in fish farming. Epidemiology
aspects of infections should be taken into account as well.
In a natural environment, the balance established during the
evolution in the host-parasite system results in the decrease
of the pathogenic effect of parasites [2]. On the contrary, the
anthropogenic activities in fish farming can modify the water
physicochemical characteristics resulting in the disruption of
the fish-parasite equilibrium. As a result, fish not only stress
but water can become more conducible to epizootics leading
to massive fish death and important economic losses [3].
The confinement of fish, the presence of a muddy vase, the
weak oxygenation, and the low depth of ponds are also factors
favoring the transmission of parasites [4-7].
Among fish parasites, Myxosporeans impedes fish growth
[8], their reproduction [4] and are involved in epizootics
responsible for massive fish deaths in farms and hatcheries
[9- 10]. In Cameroon, studies on fish myxosporeans are
essentially descriptive. Therefore, for the last decades, only
a few epidemiological data are available comprising those by
Lekeufack [11], Lekeufack and Fomena [12], Nchoutpouen, et al.
[13], and Nchoutpouen [14]. Qualitative and quantitative data
provided by epidemiology are essential in the implementation
of prevention and control strategies against myxosporean
infections. The goal of this study was to assess the prevalence
and some epidemiological aspects of myxosporean infection in
Oreochromis niloticus and Hemichromis fasciatus fishes from the
Ngoundoup ponds in Koutaba Subdivision, West Cameroon in
order to set up a database for their efficient prevention and
control.
Materials and methods
Study area and geoclimatic characteristics
Fishes were collected from June 2019 to April 2020 in
the ponds located at the village named Ngoundoup (Figure
1), Koutaba Subdivision (North Latitude: 5°37’- 5°52’, East
Longitude: 10°44’-10°54’), Noun Division, Region of WestCameroon. The average altitude is about 1276m above sea level.
Figure 1: Map showing the study area and collection site.
002
Citation: Fonkwa G, Nack J, Kouam KM, Tomedi EM, Tchoumboue J (2022) Some epidemiological aspects of Myxosporean infections in Oreochromis niloticus
(Linnaeus, 1758) and Hemichromis fasciatus (Peters, 1857), two cultured Cichlid fishes in the West - Cameroon. Int J Aquac Fish Sci 8(1): 001-009.
DOI: https://dx.doi.org/10.17352/2455-8400.000073
https://www.peertechzpublications.com/journals/international-journal-of-aquaculture-and-fishery-sciences
Climate is of the tropical mountain subset with two seasons:
a long rainy season running from March to November and
a short dry season from November to March. There are two
transitional seasons i.e. from mid - October to mid - November
and from mid-March to mid-April. The annual average
temperature ranges from 19.80°C to 22.00°C while the rainfall
varies between 1313.72 and 1988.60mm. The soil is of ferritic
type and rich in organic matter. The sub-highland forest is
often degraded by coffee plantations and other food crops [15].
Collection, examination of fishes and Myxosporeans
identification
Fishes were captured at day using fish nets and were
immediately stored in a vial containing 10% formalin solution
and transported to the laboratory for examination. Fishes were
identified as described by Stiassny, et al. [16] and examined
for the presence of myxosporeans as per Abakar [17]. Thus,
standard and total lengths were measured to the nearest
millimeter using a slide caliper. Fishes were sex- determined
after dissection.
The community structure of fishes (Table 1) reveals that a
total of 320 specimens (Figure 2) comprising 189 Oreochromis
niloticus and 131 Hemichromis fasciatus were collected. Various
organs (skin, eye, kidneys, livers, gonads, spleens, gills,
fins, buccal cavity, brain, digestive tract, gall bladder, brain)
were examined with naked eyes, then with a stereoscopic
microscope using the 10X lens to look for the cysts. Smears of
the kidneys, spleen, and gonads were made and examined at a
total magnification of 1000X with a light microscope to search
for myxospores. Cysts were crushed between a slide and a
cover glass in a drop of distilled water and their contents were
identified with the light microscope using the 100X lens. Spores
were fixed and stained with methanol and May-GrünwaldGiemsa respectively and photographed with a digital camera
(Canon Ixus brand).
Myxospores were measured with a calibrated ocular
micrometer as recommended by Lom and Arthur [18] and were
morphologically identified using the key provided by Lom and
Dyková [19,20], Eiras, et al. [21-22], Fomena and Bouix [23].
Epidemiological parameter studied and statistical analysis
The epidemiological parameter studied was the prevalence
(Pr) of infection expressed in percentage and defined as the
number of fish species infected by a given parasite species
divided by the number of fish examined [24]. The prevalence
was classified as very low (Pr<25%), low (25% ≤ Pr <50%),
high (50% ≤ Pr <75%) and very high (75% ≤ Pr ≤ 100%).
The comparison of prevalence was performed using the
Chi-square (X2) test. The Spearman correlation coefficient “r”
was calculated to determine a probable relationship between
the prevalence of parasite species and the fish size. The
significance level of the probability was p < 0.05 and the Graph
Pad Prism 5 software was helpful for analysis.
Results
Results are illustrated in Figures 3-7 and Tables 2-3.
Myxosporean fauna of fishes and prevalence of fish
species
The myxosporean fauna of fishes shown in Table 2 was
composed of 8 species of the genus Myxobolus. The prevalence
of myxosporeans species in relation to fish species illustrated
in Figure 3 reveals a high (54.38%) overall prevalence of
infection in the ponds. Irrespective of the parasite species,
both fish species were parasitized. In addition, Oreochromis
niloticus (75.13%) was significantly (X2= 25.92; p= 0.001) more
infected than Hemichromis fasciatus (24.27%). The prevalence of
parasites was very low (<25%) whatever the fish species.
Oreochromis niloticus and Hemichromis fasciatus harbored 8
and 3 myxosporean species respectively. Moreover, 5 parasite
species (M.tchadanayei, M. agolus, M. heterosporus, M.tilapiae and
M. kainjiae) were specific to Oreochromis niloticus while 3 (M.
camerounensis, M. israelensis and M. brachysporus) were common
to both fish species. In Hemichromis fasciatus, the prevalence
varied significantly (X2= 17.41; p<0.001) from 5.30 (M.
brachysporus) to 10.30% (M. camerounensis) while in Oreochromis
niloticus, Myxobolus tilapiae and M. tchadanayei exhibited
the highest (24.50%) and the lowest (0.92%) prevalence
respectively (p<0.001).
Prevalence of Myxosporean species as a function of fish
sex
The prevalence of myxosporean species as a function of fish
sex exhibited in Figure 4 reveals that, both males and females
were infected. Regardless of the fish and parasite species,
females (67.01%) were insignificantly (X2= 1.63; p= 0.201)
Table 1: Community structure of Oreochromis niloticus and Hemichromis fasciatus in Ngoundoup ponds, Koutaba Subdivision, West-Cameroon.
Class size (mm)
Fish species
Oreochromis niloticus
Hemichromis fasciatus
Total
Seasons
Sex
[25 - 75]
[75 - 125]
>125
Total
Rainy
Transitional season
Dry
MSL (mm)
♂
23
46
42
111
35
31
45
46.35 (25-200)
46.83 (26-210)
♀
15
30
33
78
27
17
34
♂+ ♀
38
76
75
189
62
48
79
46.55 (25-210)
♂
12
35
35
82
28
26
28
46.89 (25-140)
♀
9
26
14
49
17
16
16
45.13 (27-135)
♂+ ♀
21
61
49
131
45
42
44
46.26 (25-140)
♂
35
81
77
193
63
57
73
46.60 (25-200)
♀
24
56
47
127
44
33
50
46.14 (26-210)
♂+ ♀
59
137
124
320
107
90
123
46.42 (25-210)
(%)
18.44
42.81
38.75
100
33.44
28.13
38.44
Mean Standard Length (MSL) is followed in the bracket by minimum-maximum values; ♂: male; ♀: female
003
Citation: Fonkwa G, Nack J, Kouam KM, Tomedi EM, Tchoumboue J (2022) Some epidemiological aspects of Myxosporean infections in Oreochromis niloticus
(Linnaeus, 1758) and Hemichromis fasciatus (Peters, 1857), two cultured Cichlid fishes in the West - Cameroon. Int J Aquac Fish Sci 8(1): 001-009.
DOI: https://dx.doi.org/10.17352/2455-8400.000073
https://www.peertechzpublications.com/journals/international-journal-of-aquaculture-and-fishery-sciences
Table 2: Myxosporean fauna found in fishes in Ngoundoup ponds, West-Cameroon.
N°
Myxosporean species
References
1
Myxobolus camerounensis
Fomena, et al.1993
2
Myxobolus israelensis
Landsberg, 1985
3
Myxobolus brachysporus
Baker, 1963
4
Myxobolus tchadanayei
Abakar, et al. 2006
5
Myxobolus agolus
Landsberg, 1985
6
Myxobolus heterosporus
Baker, 1963
7
Myxobolus tilapiae
Abolarin, 1974
8
Myxobolus kainjiae
Obiekezie and Okaeme 1990
Table 3: Correlations between the prevalence of Myxosporean species and the fish
size.
Fish species
Myxosporean species
Oreochromis niloticus
Hemichromis fasciatus
r
p
r
p
Myxobolus camerounensis
-0.09
0.280
+0.05
0.613
Myxobolus israelensis
-0.03
0.778
+0.04
0.708
Myxobolus brachysporus
-0.01
0.948
-0.03
0.749
Myxobolus tchadanayei
+0.06
0.498
-
-
Myxobolus agolus
-0.03
0.728
-
-
Myxobolus heterosporus
0.00
0.971
-
-
Myxobolus tilapiae
-0.20
0.02
-
-
Myxobolus kainjiae
+0.09
0.294
-
-
considered seasons were favorable to fish infections. Moreover,
the overall prevalence was significantly (X2= 85.84; p<0.001)
higher during the dry season (88.76%) than the rainy (75.31%)
and transitional (20.29%) seasons. Myxobolus tchadanayei, M.
heterosporus and M. tilapiae were the sole parasites exhibiting no
significant (p>0.05) seasonal variation of the prevalence. The
comparison of the seasonal prevalence of parasites between
fish species reveals that Oreochromis niloticus was not infected
during the transitional season. On the contrary, Hemichromis
fasciatus was significantly more parasitized by Myxobolus
israelensis (24.32%) during the transitional season compared
to other seasons. In Oreochromis niloticus, the prevalence of
parasites did not show a significant seasonal variation (X2=
0.47; p= 0.92) while in Hemichromis fasciatus, parasites were
more prevalent (X2= 14.254; p<0.001) during the dry season
(28.84%) followed by the rainy (15.80%) and the transitional
seasons (10.32%).
r: correlation coefficient; p: error probability; -: no value
more infected than males (58.94%). Whether in Oreochromis
niloticus (X2= 2.12; p= 0.145) or Hemichromis fasciatus (X2= 0.08;
p= 0.782), the prevalence of parasite species did not differ
between males and females.
Prevalence of Myxosporean species in relation to fish
size class
80
Prevalence of Myxosporean species as a function of the
infection sites and fish species
70
Pre vale nce (% )
50
40
30
20
10
yx
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The seasonal prevalence of myxosporean species (Figure 7)
shows that irrespective of the fish and parasite species, all the
54.38
60
The prevalence of myxosporean species as a function
of infection sites and fish species as illustrated in Figure 6
reveals that irrespective of the fish species, only two organs
were infected namely kidneys and ovaries. In both fish species,
kidneys were infected while ovaries were the only parasitized
organs in Oreochromis niloticus. Whether between or within
fish species, the prevalence was higher for the kidneys. The
comparison of the infection sites in terms of parasites richness
shows that all the 8 myxosporean species were encountered in
the kidneys while Myxobolus kainjiae was specific to O. niloticus
ovaries.
Seasonal prevalence of Myxosporean species
O. niloticus
H. fasciatus
O. niloticus + H. fasciatus
75.13
Figure 2: Photographs of fish specimens.
a: Oreochromis niloticus Linnaeus, 1758 (bar: 13 cm);
b: Hemichromis fasciatus Peters, 1857 (bar: 4.5 cm)
24.27
As illustrated in Figure 5, fish of all size classes were
infected. Whatever the fish species, the prevalence of
myxosporean species did not significantly differ (p>0.05)
between size classes. The prevalence of Myxobolus tilapiae
(Table 3) was negatively and significantly correlated (r= -0.20;
p= 0.02) with Oreochromis niloticus size.
Parasite species
Figure 3: Prevalence of Myxosporean species in relation to fish species.
004
Citation: Fonkwa G, Nack J, Kouam KM, Tomedi EM, Tchoumboue J (2022) Some epidemiological aspects of Myxosporean infections in Oreochromis niloticus
(Linnaeus, 1758) and Hemichromis fasciatus (Peters, 1857), two cultured Cichlid fishes in the West - Cameroon. Int J Aquac Fish Sci 8(1): 001-009.
DOI: https://dx.doi.org/10.17352/2455-8400.000073
Myxobolus kainjiae
All species
55.74
Myxobolus camerounensis
Myxobolus tchadanayei
> 125
>125
Myxobolus brachysporus
Myxobolus heterosporus
Myxobolus tilapiae
All species
10.47
All species
60.71
Myxobolus heterosporus
Myxobolus tilapiae
M. kainjiae
56.79
All species
68.97
Myxobolus camerounensis
Myxobolus israelensis
Myxobolus brachysporus
All species
18.29
34.69
Myxobolus camerounensis
Myxobolus israelensis
Myxobolus heterosporus
O. niloticus + H. fasciatus
Myxobolus israelensis
Myxobolus agolus
Myxobolus tchadanayei
Myxobolus agolus
Myxobolus heterosporus
Myxobolus tilapiae
Myxobolus kainjiae
All species
58.94
67.01
005
https://www.peertechzpublications.com/journals/international-journal-of-aquaculture-and-fishery-sciences
Myxobolus tilapiae
Myxobolus tchadanayei
Female
Myxobolus heterosporus
Myxobolus brachysporus
Male
Myxobolus agolus
80
18.78
All species
Myxobolus tchadanayei
Myxobolus israelensis
H. fasciatus
Fish species
Myxobolus brachysporus
Myxobolus camerounensis
A
Myxobolus camerounensis
]75 - 125]
Oreochromis niloticus size classes (mm)
B
]75 - 125]
Hemichromis fasciatus size classes (mm)
23.33
All species
81.82
All species
70
Myxobolus kainjiae
60
Myxobolus brachysporus
50
Myxobolus agolus
40
Myxobolus tchadanayei
30
Myxobolus brachysporus
Myxobolus camerounensis
O. niloticus
[25 - 75]
Myxobolus israelenis
20
Myxobolus israelensis
10
Myxobolus camerounensis
0
Myxobolus camerounensis
Figure 4: Prevalence of Myxosporean species as a function of Oreochromis niloticus and Hemichromis fasciatus sex.
90
80
70
60
50
40
30
20
0
30
20
0
10
10
Prevalence (%)
[25 - 75]
Figure 5: Prevalence of Myxosporean species to Oreochromis niloticus (A) and Hemichromis fasciatus (B) size classes.
Citation: Fonkwa G, Nack J, Kouam KM, Tomedi EM, Tchoumboue J (2022) Some epidemiological aspects of Myxosporean infections in Oreochromis niloticus
(Linnaeus, 1758) and Hemichromis fasciatus (Peters, 1857), two cultured Cichlid fishes in the West - Cameroon. Int J Aquac Fish Sci 8(1): 001-009.
DOI: https://dx.doi.org/10.17352/2455-8400.000073
Prevalence (%)
Prevalence (%)
https://www.peertechzpublications.com/journals/international-journal-of-aquaculture-and-fishery-sciences
Infection sites
B
30
24.27
75.13
Ovaries
Kidneys
80
A
20
Pr e val e nc e (% )
P r e val e nc e (% )
60
40
10
3.50
20
0
M
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ob
M
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Parasite species
Parasite species
Figure 6: Prevalence of Myxosporean species as a function of infection sites in Oreochromis niloticus (A) and Hemichromis fasciatus (B).
Transitional season
20
0
B
15.80
20
10.32
40
Dry season
26.84
74.97
A
Pre vale nce (% )
60
Rainy season
30
53.60
10
Myxosporean species
Trans itional s eas on
es
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Dry s eas on
88.76
Rainy s eas on
C
60
40
20.29
Pre vale nce (% )
80
Myxosporean species
75.31
100
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Pre vale nce (% )
Dry season
Rainy
80
20
M
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Myxosporean species
Figure 7: Seasonal prevalence of Myxosporean species in Oreochromis niloticus (A), Hemichromis fasciatus (B), and O. niloticus + H. fasciatus (C).
006
Citation: Fonkwa G, Nack J, Kouam KM, Tomedi EM, Tchoumboue J (2022) Some epidemiological aspects of Myxosporean infections in Oreochromis niloticus
(Linnaeus, 1758) and Hemichromis fasciatus (Peters, 1857), two cultured Cichlid fishes in the West - Cameroon. Int J Aquac Fish Sci 8(1): 001-009.
DOI: https://dx.doi.org/10.17352/2455-8400.000073
https://www.peertechzpublications.com/journals/international-journal-of-aquaculture-and-fishery-sciences
Discussion
The predominance of myxosporeans of the genus Myxobolus
(8 species over 8) in the study site is well documented. The
world myxosporeans fauna is composed of about 2180 species
(62 genera) among which the genus is numerically the most
abundant with about 35% of species [20]. Kaur [25] reported 55
myxosporean species grouped in 6 genera in various organs of
wetlands and cultured carps in Punjab out of which, the genus
Myxobolus was the most represented (28 species) compared to
other genera namely Thelohanellus (18 species), Henneguya (6
species), Triangula (2 species), Neothelohanellus and Unicauda
(1 species each). The same observation was made by Anu [26]
who recorded up to 64% of Myxobolus species infecting cultured
native and exotic carps in Punjab. Abakar [17] reported 60% of
Myxobolus species in Myxosporeans fauna of Chad freshwater
fishes. Meanwhile, in Cameroon, Lekeufack and Fomena [12]
collected 54.55% of the myxosporeans of the genus Myxobolus
in the River Sangé infecting several hosts. Nchoutpouen, et al.
[13] reported 100% Myxobolus species (10 species over 10) in
Foumban fish ponds. The broad spectrum of hosts experienced
by the genus Myxobolus, its preponderance, wide geographic
distribution, and ecological plasticity might be due to the
versatility of its metabolic pathway and the genetic background
enabling it to get adapted to various biotopes.
Myxobolus camerounensis, M. israelensis and M. brachysporus
could be of stenoxenous specificity since they commonly
infected Oreochromis niloticus and Hemichromis fasciatus which
belong to the same family (Cichlidae). Myxosporean species
that were specific to O. niloticus probably might be oїoxenous
(narrow specificity). The fish/parasite specificity can be
explained by the fact that different hosts constitute different
habitat options (ecological niches) for parasites. Each parasite
is thus adapted to the host which provides a maximum resource
for the parasite survival.
The high overall prevalence of infection (54.38%) in the
ponds is in agreement with Nchoutpouen, et al. [13] who reported
a high prevalence (64.80%) in Oreochromis niloticus (Nile
tilapia) in Foumban fish ponds (West-Cameroon). Moreover,
the latter authors also observed a prevalence of 61.10% in O.
niloticus from the natural environment (Noun River). In Punjab,
34.71% of fishes were infected in three wetlands (Harike,
Kanjali, and Ropar) and 26.28% in aquaculture [25]. Anu [26]
reported 44.20% of infected native Indian carps in aquaculture.
In Egypt, Mohammed, et al. [27] recorded in the Nile River the
prevalence of 25.00% and 24.20% in O. niloticus and Tilapia zilli
respectively. In the natural environment, the prevalence of
infection is generally low (compared to the farming situation)
because the balance established during the evolution of host/
parasite system reduces the pathogenic effects of parasites [2].
The prevalence of the parasite species vary geographically [28]
as per the host species [29]. In aquaculture, the anthropogenic
activities, the confinement of fish, the presence of muddy vase,
the low oxygenation and lo water depth are factors increasing
the prevalence of parasites [4-7].
In ponds, the low water flow may result in heavy
myxosporean infections. In fact, Ray, et al. [30], Ray and
Bartholomew [31] claimed that the water flow was the most
important abiotic factor after the water temperature influencing
the transmission of myxosporeans. High flows may scour and
remove preferred oligochaete habitat, dilute infectious stages
and decrease transmission of actinospores to fish [32]. On the
other hand, lower flows encourage higher retention of spores
and transmission of myxospores to oligochaete hosts [33]
resulting in a higher prevalence of infection in both oligochaete
and fish hosts, as well as higher infection severity in fish
[32]. Actinospores transmission as well as the prevalence of
myxosporean infections are greatly reduced above a velocity
threshold of about 0.2–0.3m/s [34- 35]. If the soil of our
study area was clayey or silty, one might think that it would
favor the myxosporean infections. Indeed, silt and clay harbor
more infected oligochaetes than other substrates [36]. At the
same water flow, oligochaetes inhabiting silt or mud produce
more actinospores than those in the sand [37-38]. However,
Neudecker, et al. [39] found no significant association between
fine sediment abundance and infection severity.
The infection rate of Oreochromis niloticus (75.13%) was
significantly higher than that of Hemichromis fasciatus (24.27%).
This may be due to the difference in fish genetic background.
If we assume that the genetic background has nothing to do
with the fish’s susceptibility to myxosporean infections, then
the infection rate will not vary between fishes sharing the same
confined biotope.
The fish sex did not significantly influence the prevalence
of parasite species. The same observation was made by Abakar
[17], Milanin, et al. [40], Lekeufack and Fomena [12]. Fomena
[5] did not observe any significant difference between the
prevalence of myxosporean in male and female Oreochromis
niloticus at Mélen fish ponds in Cameroon. Viozzi and Flores
[41] also claimed that the prevalence of Myxobolus biliare in
Galaxias maculates was not sex-related. They further opined
that it is a general situation with myxosporean infection. Anu
[26] instead reported that female carps were more infected
(38.25%) compared to males (26.21%). Gbankoto, et al. [42]
thought that the prevalence of myxosporidiosis is often higher
in males than in females probably due to the fact that males
lose a huge amount of energy for testosterone synthesis,
resulting in a weaker immune system [43]. The effect of fish
sex on the prevalence of myxosporean infections is still to be
thoroughly investigated [44].
Fishes of all size classes were infected without any
significant difference in the prevalence among size classes.
Obiekezie and Okaeme [4] made the same remark. According
to Viozzi and Flores [41], Tombi and Bilong Bilong [7], and
Abakar [17], young fishes are more vulnerable to myxosporean
infections than older ones. On the contrary, Nchoutpouen, et
al. [13] outlined that in ponds, older Oreochromis niloticus were
more infected than the younger ones. As Oreochromis niloticus
grows, the prevalence of Myxobolus tilapiae decreased (r= -0.20;
p= 0.02). A similar phenomenon was observed in Finland where
the prevalence of infection of Rutilus rutilus by Myxobolus rhodei
and M. pseudodispar decreased with the fish size; this might be
due to the increase of the immune system response with the
fish size [29].
The infections of the kidneys with all the 8 myxosporean
species suggest that those organs offer suitable micro biotopes
with optimal life conditions for parasites. Since kidneys filter
007
Citation: Fonkwa G, Nack J, Kouam KM, Tomedi EM, Tchoumboue J (2022) Some epidemiological aspects of Myxosporean infections in Oreochromis niloticus
(Linnaeus, 1758) and Hemichromis fasciatus (Peters, 1857), two cultured Cichlid fishes in the West - Cameroon. Int J Aquac Fish Sci 8(1): 001-009.
DOI: https://dx.doi.org/10.17352/2455-8400.000073
https://www.peertechzpublications.com/journals/international-journal-of-aquaculture-and-fishery-sciences
blood and secrete many solutes [45], parasites converge there
for the metabolites they need, this may be the reason why they
harbored more parasite species than ovaries. The specificity
of Myxobolus kainjiae to O. niloticus ovaries probably is because
ovaries provide a suitable environment for the M. kainjiae
survive.
The prevalence was higher in the dry season than in the
rainy and transitional seasons. In Foumban ponds (Cameroon),
Nchoutpouen, et al. [13] noticed that the infection rates were
higher in the rainy season and low in the dry season. Moreover,
Sitjà and Alvarez [46] observed that in Spain, the prevalence
of Sphaeropora dicentrarchi, in Dicentrarchus labrax varied with
seasons in the fish ponds higher, being during the summer
than the autumn. Also, the prevalence of Myxidium biliaire was
reported to be higher in summer than in winter [41]. Thus
there appear to be contradictory results regarding the season
of higher infection rate suggesting that other factors may
be intrinsic (parasite and host) or extrinsic (water Physicochemical characteristics, general management of ponds)
regulate parasite prevalence. For instance, during the dry
season, the increase in water temperature and the presence
of a muddy vase raise the prevalence of the myxosporean and
the oligochaetes (definitive host). Özer, et al. [47] revealed
that mud subtracts favors rapid growth and multiplication
of oligochaetes. Consequently, during the dry season, the
definitive hosts are very abundant and their infecting stages
(actinospores) multiply rapidly. This situation is favorable to
fish infection [48].
Conclusion
The overall prevalence of myxosporean infection in the
Acknowledgment
The authors are grateful to fish farmers of Koutaba
Subdivision, West Region of Cameroon for their collaboration.
Availability of data and material
The raw data used to support the findings are available
from the corresponding author upon reasonable request.
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Citation: Fonkwa G, Nack J, Kouam KM, Tomedi EM, Tchoumboue J (2022) Some epidemiological aspects of Myxosporean infections in Oreochromis niloticus
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009
Citation: Fonkwa G, Nack J, Kouam KM, Tomedi EM, Tchoumboue J (2022) Some epidemiological aspects of Myxosporean infections in Oreochromis niloticus
(Linnaeus, 1758) and Hemichromis fasciatus (Peters, 1857), two cultured Cichlid fishes in the West - Cameroon. Int J Aquac Fish Sci 8(1): 001-009.
DOI: https://dx.doi.org/10.17352/2455-8400.000073