Larvae of Contracaecum nematode in tilapia fish (Oreochromis niloticus) from fishing grounds of northern Lake Tana, Ethiopia Moa M. Shigut 1, Anwar N. Arefainie 2 1 Livestock development and Health Agency, West Wollega, Ethiopia. 2 University of Gondar, Faculty of Veterinary Medicine, P.O. Box 346, Gondar, Ethiopia. Correspondence: Tel. +251 911 39 75 16, Fax +251 114 45, E-mail hamduanwar@yahoo.com Abstract. The study was conducted to determine the occurrence and magnitude of larvae of Contracaecum nematode infection in tilapia fish (Oreochromis niloticus). It was conducted in fishing grounds of northern Lake Tana namely Ganda, Guguba, Saban and Sandaye. Following sampling each tilapia fish was examined thoroughly for the presence of larvae of Contracaecum nematode and parasites were identified to genus level. Among 373 tilapia fish examined, 149 (39.9%) were found infected with larvae of Contracaecum spp. The larvae was recovered from the body cavity and the mean intensity was 4. Statistically no significant differences were observed in the magnitude of Contracaecum species (spp.) infection between male and female tilapia (P=0.361) and among the different fishing grounds (P=0.110). However, slightly high proportion of larvae of Contracaecum spp. was recorded in female than male, and fish sampling sites of Sandaye and Saban, where high fishing activity and abundant distribution of piscivorous (pelicans) birds were observed. The prevalence of 39.9% reported in this study seems smaller than previous similar studied conducted in Kenya and Ethiopia, it is still higher to affect negatively the production and productivity of fish in the study area. Hence the nearby experts, government officials and fishermen should work together and open their eyes on the most appropriate and strategic control options. Keywords: Contracaecum; Fishing grounds; Lake Tana; Tilapia fish. Received 27/09/2013. Accepted 10/06/2014. Introduction Fish diseases are very important aspects of modern fish farming given the enormous impact on profitability and also cause of human diseases in many areas of the world (Ruiter, 1995). Fish are harbouring a wide variety of adult and immature forms of parasites and acting either as a sole host in parasites life cycle or as one in a series of hosts (Hart and Reynolds, 2002). Contracaecum species (spp.) are in the genus Ascaridoide, family Anisakidae, and they are parasites of aquatic birds and mammals. The larvae of Contracaecum spp. occur in the body cavity and mesenteries of fish while the adult in the gut of piscivorous birds, notably pelicans, cormorants, herons and darters (Anderson, 2000). The occurrence of the parasite has been widely reported in tilapia and catfish from several African countries 33
(Khalil, 1969; Boomker, 1982). In Ethiopia Paperna (1996) and Yimer and Enyew (2003) have also reported the occurrence of larvae of Contracaecum spp. in tilapia fish. The prevalence of larvae of Contracaecum infection in fish from contaminated pond often approaches 100% (Malvestuto and Ogambo- Ongoma, 1978). However, Yimer and Enyew (2003) have reported average prevalence of 64.3% in tilapia fish from southern gulf of Lake Tana. Usually 1-4 larvae of Contracaecum parasites have been collected per fish even though there are reports of 6 per tilapia fish in Ethiopia (Yimer and Enyew, 2003) and 12 in large (200-350 g) tilapia in Kenya (Abowei and Ezekiel, 2011). The high prevalence of Contracaecum in freshwater or marine fish may affect their health. When in the stomach of the definitive host, L3 moults to become L4 and both the larvae and the adults may affect the host health negatively (Kanarek and Bohdanowicz, 2009). Larvae of Contracaecum spp. are usually affecting the marketability of commercially produced fish, thus raising a lot of public health concerns, especially in areas where raw or smoked fish are eaten (Paperna, 1996). Humans can accidentally be infected with larval stages of these nematodes, leading to a sever disease generally known as Anisakidosis (Shamsi and Butcher, 2011), a zoonotic infection characterized by stomach pains, fever, diarrhea and vomiting (Arslan et al., 1995). Consumption of live larvae in raw or undercooked fish, however, is not necessarily the only way in which the parasite can cause disease; in some cases there is evidence that occupational exposure to fish products may be sufficient to trigger an allergic response to anisakid allergens (Purello-D Ambrosio et al., 2000). This study have been conducted because no study was carried out on the epidemiology of larvae of Contracaecum spp. in the fishing grounds of northern Lake Tana, except one recorded by Yimer and Enyew (2003) in the southern gulf of Lake Tana. The objective of this study was therefore to determine the occurrence and distribution of larvae of Contracaecum spp. in tilapia fish from fishing grounds in tributaries of northern Lake Tana. Materials and methods Study area The study was conducted in the known fishing grounds of tributaries of northern Lake Tana, namely Sandaye, Saban, Guguba and Ganda (figure 1). Lake Tana (1786 m.a.s.l.) is the source of the Blue Nile River and has a total drainage area of approximately 15 000 km 2, of which the lake covers around 3200 km 2. The lake is located in the north-western highlands of Ethiopia at 12 00 N and 37 15 E and receives runoff from more than 40 rivers (Rientjes et al., 2011). The climate of the region is tropical highland monsoon with main rainy season between June and September. The air temperature shows large diurnal but small seasonal changes with an annual average of 20 C. The mean annual relative humidity (1961 2004) at Bahr Dar gauge station is 0.65 (Setegn et al., 2008). Study population Figure 1. Map of the study area Tilapia (Oreochromis niloticus), which is belonging to the family cichilidae, was the target fish species. It is the most widespread in Africa and commercially the major fish species in Lake Tana fishery. 34
Study methodology The study was cross sectional and conducted from October 2009 to March 2010. The required sample size was 373 and it was calculated based on the formula for simple random sampling indicated by Thrusfield (2005). The expected prevalence of 41.5%, 95% confidence interval and 5% precision were considered during sample size calculation. The calculated sample size was also roughly divided to the study fishing grounds based on tilapia density estimated in each fishing ground, and accordingly 95, 93, 97, and 88 tilapia fish from Ganda, Guguba, Saban and Sandaye, respectively were sampled. Fish were collected two days in a week using multi-mesh monofilament survey gillnet that is composed of five different randomly distributed mesh size-panels, ranging from 60-120 mm. Sampling days were selected by simple random sampling technique and maximum 5 tilapia fish were collected and examined from each study site for larvae of Contracaecum spp. The sex of each tilapia fish was recorded and it was determined by viewing the gonads according to Nicolsky (1963). The body cavity was also examined for the presence of larvae of Contracaecum nematode and cysts just after the removal of the entire digestive tract. The parasites were fixed in 5% formalin. Parasites were stained overnight with a weak erlich s haematoxylin solution and passed through graduated alcohol (30, 50, 70, 90% and absolute) for 45 min. to dehydrate, cleared in methyl-salicylate and mounted on a slide in Canada balsam. The larvae of Contracaecum spp. were identified to generic level based on the morphological keys stated by Yamaguti (1961) and Paperna (1996). Data analysis The prevalence rate was calculated as the number of tilapia fish positive for one or more than one larvae of Contracaecum nematode per 100 examined. The mean intensity was calculated by dividing the total number of larvae of Contracaecum spp. recovered in a sample divided by the number of hosts infected with the parasite under the study. Fisher s exact test was applied to determine the association between the variables and the presence of infection using Intercooled STATA 11.0 version. Statistical significance was considered at P-value <0.05. Results Out of 373 tilapia fish examined, 149 (39.9%) were found infected with one or more than one larvae of Contracaecum nematode. On average 4 larvae were collected per fish and they were found freely in the pericardial cavity. The recovery of larvae of Contracaecum spp. did not show significant association with sex of tilapia (P=0.361) (table 1) and fish sampling sites (P=0.110) (table 2). Table 1. Larvae of Contracaecum nematode infection with respect to sex of Oreochromis niloticus Sex Examined Positive Prevalence P- (%) value Male 211 80 37.9 0.361 Female 162 69 42.6 Total 373 149 39.9 Table 2. Larvae of Contracaecum nematode infection with respect to sex of Oreochromis niloticus Sex Examined Positive Prevalence P- (%) value Male 211 80 37.9 0.361 Female 162 69 42.6 Total 373 149 39.9 Discussion In this study the average number of Contracaecum larvae recovered in tilapia fish was found almost in agreement with the previous studies in Kenya and Ethiopia even though the overall prevalence (39.3%) was recorded much lower than those studies. In Kenya for instance, in Lake Naivasha 85% with a mean of 9 worms per fish, in Lake Baringo 70% with 5 worms per fish and in Lake Magadi 80% with a mean of 2 worms per fish were reported (Malvestuto and Ogambo-Ongoma, 1978). In Ethiopia, 59.77% in southern gulf of Lake Tana (Yimer and Enyew, 2003) and 39.67% at Lake Awassa (Zekarias and Yimer, 2007). However, the reported mean intensity of worms per fish was 6 (Yimer and Enyew, 2003). The variations observed in prevalence rates between this study and the other similar 35
studies (particularly studies conducted in Ethiopia) could be associated with variation in distribution of the definitive host piscivorous birds, the primary intermediate host copepods and/or the season the studies are conducted. Paperna (1974) mentioned that Contracaecum is linked with migration of piscivorous birds, particularly (or even only) Pelicans. Even though statistically no significant difference obtained relatively higher prevalence of larvae of Contracaecum nematode infection was recorded in female (42.6%) than male (37.9%) tilapia fish. This observation agreed with the finding of Al- Zubaidy (2009) in which female fish were generally more liable than male to infections with nematodes, cestodes, acanthocephalan, crustacean and copepod parasites (Ibiwoye et al., 2004). In this study relatively high infection rates were also observed in Sandaye (50) and Saban (41.2) than Ganda (34.7) and Guguba (34.4) fish sampling sites. These results are explained by factors related to the environment (temperature, salinity) and the presence of birds, final hosts (Dione et al., 2014). Accordingly the variation in the infection rates recorded in this study might attribute to the differences in fishing activities and load of piscivorous (pelicans) birds observed among the study sites during the study period. The present study revealed an intensive infection of Contracaecum spp. in tilapia fish in the study fishing grounds of tributaries of Lake Tana. The high prevalence of Contracaecum spp. might affect the production and productivity of the fish. Therefore further study on the epidemiology and economic impact of Contracaecum spp. infection in tilapia fish and systematic control of this parasite in the study area is advisable. Acknowledgements The authors would like to acknowledge Bahir Dar Fishery and Other Aquatic Life Research Centre for technical support and materials provided during the study period. References Abowei J.F.N., Ezekiel E.N. 2011. Trematoda and tape worms: Infections by larval and other tape worms, and nematoda in African fish. Int. J. Anim. Veter. Adv. 3:352-366. Al-Zubaidy A.B. 2009. Prevalence and densities of Contracaecum sp. larvae in Liza abu (Heckel, 1843) from different Iraqi water bodies. JKAU Mar. Sci. 20:3-17 Anderson R.C. (Ed.). 2000. Nematode Parasites of Vertebrates: Their Development and Transmission. 2 nd ed., CAB International, Wallingford. Arslan A., Dincoglu A., Guven A. 1995. The zoonoses produced by the sea foods consumption in humans. Kafkas Univ. Vet. Fak. Derg. 1(1-2):103-107. Boomker J. 1982. Parasites of South African freshwater fish. Onderstepoort J. Vet. Res. 49:41-51. Dione E.N., Diouf M., Fall J., Bâ C.T. 2014. Seasonal and spatial distribution of nematode larvae of the Genera Anisakis and Contracaecum (Anisakidae) in two populations of Mugil cephalus (Mugilidae) from Saloum and Senegal rivers. Journal of Biology and Life Science 5:41-56. Hart P.J.B., Reynolds J.D. (Eds.). 2002. Handbook of Fish Biology and Fisheries. Blackwell Publishing, Oxford. Ibiwoye T.I.I., Balogun A.M., Ogunsusi R.A., Agbontale J.J. 2004. Determination of the infection densities of mudfish Eustrongylides in Clarias(C)gariepinus and C. anguillaris from Bida floodplain of Nigeria. J. Appl. Sci. Environ. Mgt. 8(2):39-44. Kanarek G., Bohdanowicz J. 2009. Larval Contracaecum sp. (Nematoda: Anisakidae) in the Great Cormorant [Phalacrocorax carbo (L.1758)] from north-eastern Poland: A morphological and morphometric analysis. Vet. Parasitol. 166:90-97. Khalil L.F. 1969. Studies on the helminth parasites of freshwater fish of the Sudan. J. Zool. 158:143-170. Malvestuto S.P., Ogambo-Ongoma A. 1978. Observation on the infection of Tilapia leucosticte (Pisces: Cichlidae) with Contracaecum (Nematoda: Heterocheilidae) in Lake Naivasha, Kenya. J. Parasitol. 64:383-384. Nicolsky G.V. (Ed.). 1963. The Ecology of Fishes. Academic Press, London. Paperna I. 1974. Larval Contracaecum in the pericardium of fishes from East African lakes, Proc. Helminthol. Soc. Was. 41:252. 36
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