Seasonal patterns of Myxobolus (Myxozoa : Myxosporea) infections in Barbus callipterus Boulenger, 19

Journal of Research in Biology

ISSN No: Print: 2231 –6280; Online: 2231- 6299

An International Scientific Research Journal

Original Research

Journal of Research in Biology

Seasonal patterns of Myxobolus (Myxozoa : Myxosporea) infections in Barbus callipterus Boulenger, 1907 (Cyprinidae) at Adamawa - Cameroon Authors: Fonkwa Georges1,2, Efole Ewoukem Thomas1, Tchuinkam Timoléon2, Fomena Abraham3 and Tchoumboue Joseph1

ABSTRACT: For a detail understanding of the seasonal patterns of Myxobolus infections so as to elaborate control strategies, 305 Barbus callipterus specimens were sampled from May 2016 to May 2017 at Mapé River (Adamawa-Cameroon). After classical examination, the prevalence of infection was determined. Ten Myxobolus species were identified. Irrespective of the parasite species, fishes were more infected in the dry season (74.93%) than the rainy season (69.72%) without significant difference.

Institution: Seasons did not significantly influence on the prevalence of parasites in the sizes and 1. Laboratory of Ichthyology and Applied Hydrobiology, sex of various fishes’ class. However, Myxobolus ngassami was predominantly prevalent in male fishes during the dry season in contrast to the females. Regardless Faculty of Agronomy and of the organ type and parasite species, the dry season was remarkably more favorable Agricultural Sciences, University of Dschang, P.O. to the infection of organs. Mono and polyinfections occurred during the two seasons and whatever the season, the prevalence of polyinfection’s categories dropped with Box 222, Dschangthe increasing number of associated parasite species.

Cameroon.

2. Laboratory of Biology and Keywords: Applied Ecology, Vector Myxobolus, Prevalence, Season, Barbus callipterus, Mapé river, Cameroon.

Borne Parasitic and Infectious Diseases Unit, Faculty of Science, University of Dschang P.O. Box 67, Dschang-Cameroon.

3. Laboratory of General Biology, Faculty of Science, University of Yaoundé I, P. O. Box 812, YaoundéCameroon.

Corresponding author: Fonkwa Georges

Article Citation: Fonkwa Georges, Efole Ewoukem Thomas, Tchuinkam Timoléon, Fomena Abraham and Tchoumboue Joseph Seasonal patterns of Myxobolus (Myxozoa: Myxosporea) infections in Barbus callipterus Boulenger, 1907 (Cyprinidae) at Adamawa -Cameroon Journal of Research in Biology (2018) 8(1): 2413-2424 Dates: Received: 05 Jan 2018 Web Address: http://jresearchbiology.com/ documents/RA0659.pdf Journal of Research in Biology An International Scientific Research Journal

Accepted: 01 Feb 2018

Published: 15 Feb 2018

This article is governed by the Creative Commons Attribution License (http://creativecommons.org/ licenses/by/4.0), which gives permission for unrestricted use, non-commercial, distribution and reproduction in all medium, provided the original work is properly cited.

2413-2424 | JRB | 2018 | Vol 8 | No 1

www.jresearchbiology.com

Fonkwa et al., 2018 INTRODUCTION Myxosporeans

Fish sampling and identification of Myxosporeans are

mainly

fish

parasites

species

(Fomena et al., 2010; Eiras et al., 2010). Their

Fishes were harvested monthly from fishermen

pathogenic effects entail the depression of fish growth

during the study period i.e. May 2016 to May 2017.

(Longshaw et al., 2010), reproduction (Obiekezie and

They were captured both at the day and night using fish

Okaeme, 1990) and the massive fish deaths (Gbankoto

nets and fishing canes. On the field, specimens were

et al., 2001; Feist and Longshaw, 2005). Lom and

immediately stored at 10% formalin solution and

Diková (2006) reported that among about 2180

transported to the laboratory for examination. Overall

Myxosporeans species (62 genera) composing the world

305 fish samples (159 males against 146 females) were

of Myxosporeans fauna, the genus Myxobolus Bütschli,

caught. The standard lengths ranged from 52 to 110 mm

1882 was numerically the most abundant with 31% of

with an average of 94.66 mm. Fishes were categorized

species.

into 3 class sizes of 20 mm amplitude each. The modal In Africa, researches emphasize more on

Myxosporeans systematic than its seasonal dynamics

class i.e. [70 - 90] represented 64.92% of sampled fishes.

(Folefack, 2010; Abakar, 2006). This is questionable

Amid the laboratory phase, identification and

because, the water physico-chemical characteristics

examination of fishes were done as per Stiassny et al.

variation resulting from the seasonal change may lead to

(2007) and Abakar (2006) respectively. Consequently,

the disruption of host/parasite equilibrium causing fish

standard and total lengths were estimated to the nearest

stress and deaths (Bilong and Jeannette, 2004). The

millimeter utilizing a slide caliper of stainless brand and

objective of the study was to assess the seasonal

the sex decided after dissection. External organs (fins,

patterns of Myxobolus infections in an economical and

skin, scales and eyes) and internal organs (gills, spleen,

dietary fish namely B. callipterus in order to boost its

kidneys, intestines, gall bladder, stomach and gonads)

production.

were analyzed with naked eyes and after that with Motic stereoscopic microscope at 10X to search for the

MATERIALS AND METHODS

macroscopic cysts. Three smears of kidneys, spleen and

Study Area

gonads were made (anterior, medium and posterior

Fishes were captured at the MAPE River in a

region) and were analyzed at a total magnification of

village named MGBADJI (6°00’- 6°20’NL and 11°20’-

1000X with a light microscope keeping in mind the end

11°40’ EL). The latter belongs to Bankim subdivision,

goal to identify spores. Cysts were crushed amongst

Adamawa – Cameroon Region. The average altitude is

slide and cover glass in a drop of distilled water and

about 724m above the sea level while the soil is a

their contents were identified with the light microscope

mixture of clay and sand. The climate is of tropical

at 1000X. After fixation of spores with methanol, they

Soudano-guinean type with a long rainy season running

were stained with May-Grünwald-Giemsa and snapped

from March to November and a short dry season from

with digital camera (Canon Ixus mark). Myxosporeans

November to March. The annual average temperature is

species were distinguished by Lom and Arthur (1989).

about 23°C whereas the rainfall ranges between 1500

Parasitological parameter studied

and 2000 mm (Olivry, 1986).

The prevalence (Pr) of infection conveyed in percentage was the proportion between the quantity of fish's species infected by a given parasite species and

2414

Journal of Research in Biology (2018) 8(1): 2413-2424

Fonkwa et al., 2018 the number examined (Bush et al., 1997).

Parasites

Whatever the season, no principal parasite was

were qualified as principal (Pr > 50 %), intermediate (10

recorded. Myxobolus pharyngeus appeared only during

% ≤ Pr ≤ 50 %) and scarce (Pr < 10 %) (Valtonen et al.,

a single season. On the one hand, during the rainy

1997).

season, prevalences were significantly higher (X2 =

Statistical analysis

58.14; P < 0.001) with M. pseudodispar and lower in

The comparison of prevalences was performed 2

M. muelleri. On the other hand, M. ngassami was the

by the Chi-square (X ) test. The significance level was

most prevalent during the dry season (X2 = 68.46; P <

P < 0.05 and the Graph Pad Prism 5 software was used

0.001) while M. pharyngeus was absent. The sole

for analysis.

parasite species showing seasonal significant variation of prevalence was Myxobolus mapei. The latter being more prevalent (X2 = 4.00; P < 0.05) in the dry season

RESULTS The results are illustrated on Table 1 and

than in the rainy season.

Figures 1 to 7.

Prevalence of infection as a function of class size and

Seasonal prevalence of Myxosporeans species

seasons

The myxosporeans fauna recorded (Figure 1)

The prevalence of infection as a function of

was composed of 10 Myxobolus species. The seasonal

class size and seasons (Figure 3) shows that fishes were

prevalence of Myxosporeans species (Figure 2 ) reveals

infected in all the three class sizes during the dry and

that, irrespective of the parasite species, fishes were

rainy seasons. Whatever the class size, the prevalence

more infected in the dry season than in the rainy season,

did not differ between seasons (P > 0.05). Whether in

2

however without significant difference (X = 0.77; P =

the rainy season or the dry season, the higher prevalence

0.380). During the rainy season three parasite species

was recorded in the class 90-110 mm, however without

were intermediate against five during the dry season.

any significant difference (X2 = 1.40; P = 0.237).

F

C

B

A

G

H

E

D

I

J

A : Myxobolus tchadanayei Abakar et al., 2006 (x 1500);

B : Myxobolus mapei Fonkwa et al., 2017 (x 1200);

C : Myxobolus muelleri Bütschli, 1882 (x 1500);

D : Myxobolus ellipsoides Thélohan, 1982 (x 1500);

E : Myxobolus pseudodispar Gorbunova, 1936 (x 1500);

F : Myxobolus pharyngeus Parker et al., 1971 (x 1500);

G : Myxobolus tchoumbouei Fonkwa et al., 2017 (x 1000); H : Myxobolus umidus Carriero et al., 2013 (x 1500); I : Myxobolus sessabai Lekeufack et al., 2017 (x 1500);

J : Myxobolus ngassami Lekeufack et al., 2017 (x 1500)

Figure 1. Spores micrographs of Myxobolus species studied Journal of Research in Biology (2018) 8(1): 2413-2424

2415

Fonkwa et al., 2018

90 80

Prevalence (%)

Prevalence (%)

70 Rainy season

60

Dry season

50 40 30 20

Total

M. ngassami

M. sessabai

M. umidus

M. tchoumbouei

M. pharyngeus

M. pseudodispar

M.ellipsoides

M. muelleri

M. mapei

0

M. tchadanayei

10

Parasite species

Figure 2. Seasonal prevalence of Myxosporeans species

150

Prevalence (%) (%) Prevalence

Rainy season

Dry season

100

50

0

[50 - 70]

]70 - 90] Class size (mm)

]90 - 110]

Figure 3. Prevalence of infection as a function of class size and seasons 2416

Journal of Research in Biology (2018) 8(1): 2413-2424

Fonkwa et al., 2018 Seasonal prevalence of parasite species as a function

of seasons (Figure 5) illustrates that, organs were

of class size

infected during both the dry and the rainy seasons.

The seasonal prevalence of parasite species as a

According to the seasonality of infections, organs are

function of class size is illustrated on Figure 4. It

grouped into three categories: those infected only in the

appears that, in term of species number, whatever the

rainy season (gills), the dry season (fins) and those

class size, parasite species occurred more in the rainy

infected during the two seasons (operculum, skin,

season apart from the class size 50-70 mm, where 8

kidney and liver). Regardless of the organ type, the dry

species were recorded both in the dry and the rainy

season was remarkably (P < 0.05) more favorable for

seasons. During the dry season, the higher prevalence

organ infection. Although kidneys were the most

(P < 0.05) was noticed for Myxobolus ngassami in the

infected organs during both the rainy (X2 = 308.60; P <

class [90 - 110] while in the rainy season the higher

0.001) and the dry seasons (X2 = 392.20; P < 0.001), no

(P < 0.05) prevalence (M. pseudodispar) was observed

significant difference of prevalence was observed.

in the class 70 - 90 mm. In this latter class, Myxobolus

Prevalence of parasite species as a function of organs

ngassami was the sole parasite exhibiting a very

and seasons

2

significant (X = 8.55; P < 0.01) variation of prevalence

As shown on Figure 6, the prevalence of

between the two seasons. Moreover, it was more

parasite species fluctuated according to seasons and

prevalent in the dry season than in the rainy season.

organs. Fins and gills were infected only during a single

Prevalence of parasite species as a function of hostâ&#x20AC;&#x2122;s

season by one parasite species. Kidneys were the only

sex and seasons

organs where intermediate species were found contrary

The prevalence of parasite species as a function

to other organs harboring scarce parasite species. In the

of hostâ&#x20AC;&#x2122;s sex and seasons (Table 1) shows that

operculum, the two seasons were not only favorable to

independently of the parasite species, male fishes were

the occurrence of Myxobolus mapei but also, its

more infected in the rainy season than the dry season

prevalences were the highest (P < 0.05) compared to

2

(X = 0.06; P = 0.812) contrary to females mostly

those of other parasite species. In the kidneys, apart

infected during the dry season (X2 = 0.01; P = 0.909).

from M. pharyngeus, all parasite species appeared

2

Whether in the rainy season (X = 0.30; P = 0.586) or 2

during both the dry and rainy seasons. The prevalence

dry season (X = 0.05; P = 0.822), the prevalence did

of Myxobolus ngassami in the kidneys was about twice

not vary significantly between males and females.

higher in the dry season than in the rainy season

When parasite species are taken into account, it

(X2 = 7.82; P < 0.01). Meanwhile, M. pseudodispar

appears that in both males and females, M. ngassami

exhibited the higher prevalence (P > 0.05) during the

was the only parasite exhibiting a significant difference

rainy season.

(P < 0.05) in prevalence between the two seasons.

Seasonal prevalence of mono and polyinfections

Moreover, it was more present in male fishes during the

The

seasonal

prevalence

of

mono

and

dry season contrary to the females. No matter the season

polyinfections is summarized on Figure 7. It appears

and the fishâ&#x20AC;&#x2122;s sex, the prevalence fluctuated very

that during both the dry and the rainy seasons, fishes

significantly (P < 0.001) between parasite species.

were

Percentage of infected organs as a function of

(monoinfection)

seasons

(polyinfection). The monoinfections were more frequent

The percentage of infected organs as a function Journal of Research in Biology (2018) 8(1): 2413-2424

infected

by and

a

single more

parasite

than

one

species species

during the rainy season than the dry season (X2 = 0.79; 2417

2418

0 00

ngassami ngassami M.M.

5

Class [50 - 70]

M. ngassami M. ngassami

M. ngassami M. ngassami

5

ngassami M. M. ngassami

10

M. sessabai M. sessabai

15

sessabai M. M. sessabai

Class ]70 - 90]

M. umidus M. umidus M. sessabai M. sessabai

20

umidus M.M. umidus

M. M. pharyngeus M. pharyngeus tchoumbouei M. tchoumbouei

Rainy eason on Rainy season Rainy sseas

sessabai M.M. sessabai

M.M.umidus umidus

Class]70 - 90]

M.M. M. tchoumbouei umidus umidus M.tchoumbouei

Parasite species Parasite species Parasite species Parasite species

M. tchoumbouei M. tchoumbouei

M. pharyngeus M. pharyngeus

Parasite spe cie s

M. pharyngeus M. M. pseudodispar pseudodispar M.pharyngeus

Class [50 - 70]

Parasite spe cie s

M. tchoumbouei M. tchoumbouei

pharyngeus M. M. pharyngeus

Parasite species

M. pseudodispar M. pseudodispar

M. pseudodispar M. pseudodispar M. ellipsoides M. ellipsoides

M. muelleri

Dry s eas on

M. pseudodispar

Dry season

M. ellipsoidesM. muelleri M. ellipsoides

Rainy s eas on

M. pseudodispar

Dry season

M. ellipsoides M. ellipsoides

10

M. ellipsoides

Rainy season

muelleri M. M. muelleri

Rainy season

M. ellipsoides

M. muelleri

10 M. mapei M. mapei

10

M. muelleri

15

M. muelleri M. muelleri

15

M. mapei

000

M.M.mapei mapei

15

M. mapei

15

M. tchadanayei M. tchadanayei

M. mapei M. mapei

000

M. tchadanayei

00

(%)(%) (%) Prevalences Prevalences Prevalences

55

M. tchadanayei M. tchadanayei

10 10

M. tchadanayei M.tchadanayei

Prevalences (%) (%) (%) Prevalence Prevalences

15 15

M. tchadanayei

(%) PrevalencePrevalences (%) (%) Prevalences

Prevalence (%) Prevalence (%)

Class [50 - 70]

Rainy season Dry season

Fonkwa et al., 2018

Class [50 [50 -- 70] 70] Class

Class [50 - 70]

Class [50-70] Dryseason eason on Dry sseas Dry

10

5

5

Parasite species Parasite species Class ]90 - 110]

150

Class ]90 - 110]

100

5

50

Parasite Parasitespecies species

Figure 4. Seasonal prevalence of parasite species as a function of class size (mm)

Journal of Research in Biology (2018) 8(1): 2413-2424

Fonkwa et al., 2018 Table 1. Prevalence of parasite species as a function of hostâ&#x20AC;&#x2122;s sex and seasons Males S. No Parasite species

Seasons Rainy Dry 79* 80* 8.86 2. 50

Females X

1

M. tchadanayei

2

M. mapei

6.33

11.25

3

M. muelleri

0.00

4

M. ellipsoides

5

2

P

Seasons Rainy Dry 63* 83* 9.52 7.23

X2

P

0.25

0.617

3.01

0.083

1.20

0.274

4.76

13.25

2.98

0.084

0. 00

-

-

1.59

1.20

0.04

0.844

5.06

2. 50

0.72

0.396

6.35

1.20

2.87

0.091

M. pseudodispar

20.25

10.00

2.38

0.123

14.29

12.05

0.16

0.691

6

M. pharyngeus

2.53

0. 00

2.05

0.152

0.00

0.00

-

-

7

M. tchoumbouei

12.66

12.50

0.00

0.980

9.52

9.64

0.00

0.981

8

M. umidus

11.39

15.00

0.45

0.502

12.70

12.05

0.01

0.906

9

M. sessabai

2.53

3. 75

0.19

0.660

1.59

4.82

1.13

0.288

10

M. ngassami

5.06

16.25

5.21

< 0.05

3.17

13.25

4.49

< 0.05

Total

50.63

48.78

0.06

0.812

46.03

46.99

0.01

0.909

X2 37.17 41.52 P < 0.001 < 0.001 *: number of examined fishes; -: no value; P : error probability

23.49 30.61 < 0.001 < 0. 001

P = 0.374) contrary to polyinfections (X2 = 0.72;

combinations. No matter the season, their frequencies

P = 0.397). Whatever the season, four categories of

dropped very significantly (P < 0.001) with the

polyinfections were recorded namely bi, tri, tetra and

increasing number of combined parasite species.

pentaspecific i.e. respectively 2 to 5 parasite species Rainy season

Dry season

60

40

Target organs

Total

Liver

Kidneys

Gills

Fins

0

Skin

20

Operculum

organs ofofinfected Percentage infected organs Percentage

80

Figure 5. Percentage of infected organs as a function of seasons Journal of Research in Biology (2018) 8(1): 2413-2424

2419

0

2420

Class[50 [50 70][50 - 70] Class Class - -70]

00 Parasite species

Parasite Parasitespecies species

0

Parasite species

2

Parasitespecies species species Parasite Parasite

Parasite species

Parasite species

1

10

15 14 13 12 11 10 9 58 7 6 5 4 3 2 1 00

Parasite species Parasite species

Skin

Skin

0

ngassami M.M.ngassami

Dry season

sessabai M.M.sessabai

Liver

Rainy season

umidus M.M.umidus

Dry season Dry Dryseason season Dry season Dry season

tchoumbouei tchoumbouei M. M.

Rainy Rainyseason s eas on Dryseason s eas on Dry

pharyngeus M.M. pharyngeus

1

Prevalence (%) (%) Prevalence

5

pseudodispar M. M. pseudodispar

Dry season

ellipsoides M.M. ellipsoides

Parasite Parasite species Parasite species Parasite species Parasite species Parasite speciesspecies M. ngassami

15

M.M.muelleri muelleri M. ngassami

Class [50 - 70]

M. sessabai

00

M.M.mapei mapei M. sessabai

Operculum Operculum

tchadanayei M.M. tchadanayei M. umidus

Rainy season Parasite species

M. tchoumbouei

Prevalences (%)

Prevalence (%) (%) Prevalence

5

M. pharyngeus

M. ngassami M. ngassami M. ngassami M. pseudodispar

3

(%) Prevalence(%) Prevalence

Dryseason season Dry Dry season

Liver

ngassami ngassami M. M.

0

M. ngassami M. ngassami M. sessabai

00

M. sessabai sessabai ellipsoides M.M.

(%) Prevalences (%) Prevalence (%) Prevalence

10

M. sessabai sessabai sessabai M.M. M. umidus

10

umidus umidus M. M. umidus M.muelleri M.

15

M. umidus M. umidus M. tchoumbouei

Dry Dryseason season

M. tchoumbouei M. tchoumbouei M. mapei

Rainy Rainyseason season

pharyngeus M. M. tchoumbouei pharyngeus M.tchadanayei M.

Class Class[50 [50- -70] 70]

M. mapei muelleri M. muelleri M. M. tchadanayei muelleri M.tchadanayei M. ellipsoides M. ellipsoides M. M. mapei M. ellipsoides pseudodispar M. pseudodispar M. pseudodispar M.M. muelleri M. pseudodispar pharyngeus M. M. pharyngeus ellipsoides M.pharyngeus M. tchoumbouei M. tchoumbouei M. tchoumbouei M. pseudodispar M. M. tchoumbouei umidus M. umidus M. M. pharyngeus M.M.umidus sessabai sessabai M. sessabai M. M. tchoumbouei M. sessabai ngassami M. M. ngassami M. ngassami umidus M. M. ngassami

000 0

M. tchoumbouei M. tchoumbouei M. tchoumbouei M. pharyngeus

1

Prevalences (%)

555 5

M. pharyngeus M. pharyngeus M. pseudodispar

5

(%) Prevalence (%) Prevalence

Prevalence (%) (%) Prevalence

tchadanayei M. tchadanayei M. M. tchadanayei mapei M. mapei M.

10 10 10 10

M. pseudodispar M. pseudodispar

M. ellipsoides M. ellipsoides

(%) Prevalences (%) Prevalences Prevalences (%) 15 15 15 15

M. pseudodispar M. pseudodispar M. ellipsoides

M. ellipsoides M. ellipsoides M. muelleri

Rainyseason season Rainy Rainy season

M. muelleri M. muelleri

M. mapei M. mapei

5

M. muelleri M. muelleri M. mapei

M. mapei M. mapei M. tchadanayei

Class [50 - 70] Class [50 -- 70] 70] Class [50 Class [50-[50 70] Class - 70]

Rainy season Rainy season Rainy season Rainy seasonRainy season

15

Fonkwa et al., 2018

Fins Fins

1

2

Class 0 [50 - 70] M. tchoumbouei M. tchoumbouei Parasite species

Parasite species

Kidneys Kidney

Parasitespecies species Parasite

Gills Gills

1

Parasite species

M. M.tchadanayei tchadanayei Parasite species

Figure 6. Prevalence of parasite species as a function of organs and seasons

Journal of Research in Biology (2018) 8(1): 2413-2424

Fonkwa et al., 2018 50 45 40 Rainy season

Dry season

Prevalence (%)

35 30 25 20 15 10

Pentaspecific

Tetraspecific

Trispecific

Bispecific

Polyinfections

0

Monoinfections

5

Mono and polyinfections Mono and polyinfections

Figure 7. Seasonal prevalence of mono and polyinfections melanotheron in Bénin was higher in the dry season. In

DISCUSSION Irrespective

the

the fishes Ctenopoma petherici, Clarias pachynema and

prevalence of infection did not differ between seasons.

Hepsetus odoe from the river Sangé (Cameroon),

This may be due to the insignificant variation of water

Folefack and Fomena (2013) showed that Myxobolus

physico-chemical characteristics with the seasons.

sp2 occurred mostly during the dry season whereas M.

Based on season, parasites were grouped into three

petrocephali, M. nkamensis and M. gariepinus were

categories: those occurring mostly during the dry season

more frequent in the rainy season. Abakar (2006)

(category A), the rainy season (category B) and those

asserted that, in the river Chari (Chad), Myxobolus

occurring without seasonality (category C). The results

brachysporus and M. camerounensis were more present

of category (A) parasites were explained by Obiekezie

in Oreochromis niloticus during the dry season than the

and Okaeme (1990). In fact, those authors thought that

rainy season. The explanation being the pollution of

during the dry season, the high temperature of water and

Chari river by factories installed in Moundou and Sarh

mud can encourage the infection with myxosporeans.

(Chad towns). The pollution was significant during the

According to Uspenskaya (1995), when myxospores

dry season because of the intensive water evaporation

sink in water, they undergo aging and maturation in the

and this could negatively affect the actinospores. This

mud or sludge in order to parasitize new hosts.

pollution is also noticed in Mapé river because

Gbankoto et al. (2001) indicated that the prevalence of

neighboring population dump refuse in the water and

Myxobolus sp. and Myxobolus zillii which are gills

use nitrated fertilizers for agriculture. As for the

parasites

category B parasites, Abakar (2006) claimed that

for

of

Tilapia

the

parasite

zillii

and

species,

Sarotherodon

Journal of Research in Biology (2018) 8(1): 2413-2424

2421

Fonkwa et al., 2018 Sarotherodon galilaeus and O. niloticus were more

two seasons were favorable to the mono and

infected during the rainy season in Chad. His

polyinfections and whatever the season, the prevalences

explanation was based on Lausanne (1988) literature.

of polyinfection categories dropped with the increasing

So, during the rainy season, flood water dissolves soil

number of associated parasite species. This observation

minerals and organic matters accumulated during the

may be due to the interspecific competition between

dry season. This will encourage the growth of planktons

parasite species. The higher the number of associated

and algae which serve as food for fishes. Actinospores

species, the higher the intensity of interspecific

being stuck on this food, fishes get infected by

competition due to resources shortage and thus lower

consuming them. The case of category (C) is similar to

the prevalence.

that noticed by Bilong and Jeannette (2004) and Abakar (2006). According to them, some myxosporeans species

CONCLUSION

are present in the fishes throughout the year; others

The seasonal patterns of Myxobolus infections

appear once in a year whereas some exhibit two or three

in Barbus callipterus were affected by the parasite

peaks of infection each year (Blazer et al., 2003).

species, the host’s sex, class size and the target organ.

Oligochaetes being intermediate hosts in myxosporeans

The recorded data are useful for elaborating control

life cycle (Markiw and Wolf, 1983) the seasonal

strategies.

variation of parasitism by myxosporeans could be due to the seasonal supplying of actinospores by oligochaetes

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