OCCURRENCE AND PREVALENCE OF PARASITES ASSOCIATED WITH Gnathonemus senegalensis IN APODU RESERVOIR , MALETE , NIGERIA

The prevalence of ectoand endo-parasites of Gnathonemus senegalensis (Trunkfish) was determined with the view of quantifying the helminthic burden in Apodu reservoir, Malete. A total of 150 fish of G. senegalensis were caught with gill nets and cast nets between November 2017 and April, 2018. The fish were transported to the Parasitology laboratory, Kwara state University Malete, for parasite examination. The result shows a prevalence rate of 42% (n=150) with Camallanus sp. and Capillaria sp. having prevalence rates of 11.1 % and 60.32%, respectively. Diphyllobothriumlatum, Acanthocephalan sp., Neascus sp., Tetrahymena sp. and Chilodonella sp. had the prevalence rates of 46.03%, 20.63%, 30.16%, 19.05% and 20.63%, respectively. The ranges of physico-chemical parameters of the water body were: temperature (26.4 -26.9 oC); conductivity (66 – 83 μs/cm); pH (7.54 7.98); transparency (110 -402 cm); water current (0.04 -0.42 m/s) and total dissolved solids (34 – 44 ppm). The findings suggest that the observed parasitic infections may adversely affect the economic value of G. senegalensis and if not well managed, could also infect human beings who consume the fish.


Introduction
Gnathonemus senegalensis (Trunkfish) is recognized by the possession of upward pointing pectoral fins, narrow gill openings and a layer of muscle covering the opercula bone (Holden & Reed, 1972).They are normally caught in bottom nets, an indication that they are bottom feeders.These fish are generally classified as carnivores or predators feeding mainly on aquatic insects, smaller crustaceans and worms (Adebisi, 1978).
Transmission of parasites to humans through freshwater fish had been reported since fish parasites and diseases are very relevant issues confronting fishery biologists (Ravichandran et al., 2007).Human activities and poor environmental conditions often subject fish to parasitic and other diseases (Biu et al., 2014).Fish parasitic infestations are common in the tropics (Roberts & Janovy, 2009;Soliman & Nasr, 2015), with various parasites being associated with different fish species.The prevalence of such infections is dependent on the nature of the ecosystems and fish susceptibility and result in considerable economic losses in the fisheries industry (Biu & Nkechi, 2013).Thereforefish parasitic diseases can be considered as one of the most detrimental factors to the success of the aquaculture industry (Paperna, 1996;Keremah & Inko-Tariah, 2013).
Community diversity and parasitic burden is known to be affected by the season, age, sex and environmental factors.Environmental factors such as pH, dissolved oxygen, extent of habitat and the proximity to a lake is known to influence parasite species richness in the host population (Karvonen et al., 2003).
Therefore, this study sought to determine the prevalence of ecto-and endoparasites in Apodu reservoir using the fish Gnathonemus senegalensis with the view of quantifying the helminthic burden and to evaluate the relationship between parasite burden and sex of fish and the water quality in the Apodu reservoir.

Study Area
The Apodu reservoir (Figure 1) lies between the longitude 8 o 45"25.9"N,8 o , 45'27.7"N and latitude 4 o 27'41.4"E, 4 o 27'35.5"E.It was constructed in 1980 with re-impoundment of the dam being carried out in 2016 to ensure water availability to Malete and other villages around it (Oladipo et al., 2018).The location of the reservoir falls within the Guinea savanna region of Nigeria which is characterized by two seasons -dry (November to March) and rainy (April to October) seasons.The reservoir is 560 m long and 400 m wide, has a depth of 8.2 m and the surface area of about 15 hectares (Oladipo et al., 2018).

Sample Collection
A total 150 Gnathonemus senegalensis fish (Figure 2) were collected from Apodu reservoir, Malete, using gill nets and cast nets, set in the evening and harvested early morning, during November 2017 to April 2018.The fish were identified using the keys by Olaosebikan & Raji (1998) and Idodo-Umeh (2003).They were immediately transported in ice to the Parasitology laboratory, Kwara State

University
Malete, for further examination.

Water Quality Analyses
Selected physicochemical parameters of the surface water were measured in situ using a Hanna portable combined waterproof tester model HI 98129.The measured parameters included electrical conductivity, temperature, pH and total dissolved solids.Transparency levels were also measured using the secchi disc with a calibrated rope attached while water velocity was measured using floatation method.

Sex Determination and Examination of fish parasites
The sex of the fish was determined by observing the genital pore and the presence or absence of testes or ovaries as apparent through examination under the microscope.The scales, fins, opercula, eyes and gills of freshly caught fish were examined for ecto-parasites with the aid of a hand lens and microscope.The ectoparasites associated with fins were collected by severing the structures and placing them in a petri dish, and additing 0.9% of saline water, which was then viewed under a dissecting microscope.The parasites were picked and treated with 0.25 % aqueous formalin for 30 minutes and allowed to settle for 15 to 30 minutes.Using a dissecting microscope, the parasites were pipetted into alcoholformalin-acetic acid (AFA) according to their taxonomic categories and fixed and preserved in 70 % alcohol (Upton, 2003).The gut was also examined for endoparasites, which were also fixed and preserved.The parasites were shaken in cold 4% formaldehyde until they died.They were then fixed in FAA (5% formal -90% alcohol -15% glacial acetic acid) for 2 hours prior to staining.The parasites were stained in aceto-carmine solution and mounted on permanent slides using Canada Balsam.Parasite identification was done by comparison of distinctive body shapes and the morphological features of the collected specimens and those described in literature and using the identification key modified from Frimeth (1994).

Data Analyses
The Incidence, and Intensity of parasitic infections, Density and Percentage of parasites and the Parasitic Index were calculated using the following equations (as used by Poulin & Rohde, 1997).

Results
Of the 150 fish of Gnathonemus senegalensis examined 63 samples were infested with parasites.Table 1 shows fish species examined in relation to sex, body weight and body length and the number infested; Male fish had a higher number of infections 24 (46.15%) in relation to number of fish examined while the female fish recorded 39 (39.80%).An infection rate of 52 % was observed in fish in the weight range of 31 -40 g while the fish with the least number of infections was recorded in the range 51 -60 g.Similarly, the highest number of infections ( 51) was observed in fish with the body lengths in the range of 15.6 -21cm.
Table 2 shows monthly reports of fish samples examined including the percentages of the number infested, incidence and prevalence.The month of April had the highest prevalence and incidence with 62 fishes being infected giving the values of 98.41% and 41.33% for prevalence and incidence respectively.December had the lowest prevalence and incidence with 15 infected fishes (23.80% and 10%).The percentage incidence and prevalence of the parasites recorded during the study were 95.33 and 226.98 %, respectively.
The study revealed that a total of 10 species of parasites was recovered from the fish examined at the end of the sampling period (see Table 3).Seven species of parasites were recorded in the months of November and December 2017 with a total number of 19 and 13 individual parasites being recorded respectively in the two months.Five species were recovered in the months of January, February and March with a total of 16, 16 and 15 parasites respectively recorded in each of the months.The analysis for the incidence, intensity, density and index of parasitic infestations were carried out and the results are presented in Table 4. Capillaria sp. had the highest incidence rate (25.33%) while both Dactylogyrus sp. and Gyrodactylus sp. had the lowest incidence rate of 4%.
The intensity rate for Camallanus sp. was recorded to be 8.57 % while the lowest intensity rate was recordhe highest density was in Chilodonella sp.(0.86%) while both Dactylogyrus sp. and Gyrodactylus sp. had the lowest desity values (0.04%).The physicochemical factors of water that were recorded during the study period are shown in

Discussion
The present study shows a low-average infection rate of the sampled fishes from the Apodu reservoir, Malete, with all parasites recovered being endo-and ectoparasites representing nematodes, cestodes, trematodes, monogeneans and protozoans.In the study, the results obtained from the examination of the occurrence of helminthes and protozoan parasites in relation to the sex of the host showed that more males were infected with helminthes parasites.This infestation may be due to differential feeding habits and as a result of different degrees of resistance to parasitic infections (Ayanda, 2009).This findings show that, the higher infection in smaller fishes increases the activities of the intestinal parasites that contributes to a decrease in body weight which is consistent with the findings of Oniye et al. (2004).
The number of nematodes isolated was higher than that of cestodes, trematodes, protozoans and monogeneans.This agrees with the findings of Akinsanya et al. (2007) describing nematodes to be a body cavity parasite known also to penetrate subcutaneous tissues.Capillaria sp. in this study had the highest prevalence in Gnathonemus senegalensis which may be as a result of its feeding habit in that digestive activities take place in the intestine leading to the release of parasites in food particles (Jenyo, 2011;Ekanem et al., 2011).Acanthocephalans were found in the intestine of the examined fish which agrees with the findings of Olurin & Somorin (2006) reported for fishes from the Owa stream.A low rate of Dactylogyrus sp. and Gyrodactylus sp.found on the gills and body surface, respectively, could be attributed to the continuous movement of water currents over the gills, skin and fins.
Occurrence of parasites varies across months which could be due to changes in host -parasite relationships and abiotic factors such as transparency, temperature, water current and pH, which would in turn be due to changes in the host's feeding habitats in relation to physical factors of the water body.Such changes will then contribute to temporal variations in the prevalence and intensity parasites.
The prevalence of gastrointestinal helminthes and protozoans in Gnathonemus senegalensis is high and may bring about a reduction in the economic value and productivity of these fish in Apodu reservoir.Hence, it is important to know how such parasitic infestations could affect fish productivity, their market value and palatability.

Figure 1 .
Figure 1.Map of the study area Incidence = (No. of parasites/ total host examined) X 100 Intensity = (No. of infected host/ No of parasites) Density = (No. of parasite collected in a sample/ total host examined) Index = (No. of parasites x No. of infected host/ total host examined) Percentage = (No. of parasite/ No. affected) X 100

Table 1 :
Occurrence of helminthic and protozoan parasites in relation to sex, body weight and body length of Gnathonemus senegalensis (Capillariaand Camallanus) in the intestine and trematodes (Neascus sp. and Acanthocephalan sp.) in the skin, intestine and gill, protozoans (Tetrahymena sp. and Chilodonella sp.) and monogeneans (Dactylogyrus sp. and Gyrodactylus sp.) in in the skin and gills and the cestode (Diphyllobothrium sp.) found in the intestine.The highest parasitic load was recorded in April 2018 [62 individuals, 98.41%] while both December 2017 and March 2018 recorded the lowest (15 individuals, 23.80%).Capillaria sp. has a high prevalence rate of 38[60.32%],followed by Neascus sp. with 19[30.16%]while the monogeneans (Dactylogyrus sp. and Gyrodactylus sp.) have the least prevalence of 6(9.52%).

Table 2 :
Monthly variation in the prevalence and incidence of parasites in Gnathonemus senegalensis Sri Lankan Journal ofBiology 4(1) January 2019

Table 3 :
Monthly variations in the prevalence of helminthic and protozoan parasites in Gnathonemus senegalensis

Table 4 :
Prevalence, incidence and intensity of infected Gnathonemus senegalensis in the Apodu reservoir

Table 5 :
Mean physicochemical parameters of the Apodu reservoir during the sampling periods

Table 6 :
Correlation between physicochemical parameters, number of fish infested and the number of parasite