Snail diversity and associated digenetic trematode Cercariae at Aquaculture Research and Development Center-Kajjansi
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Trematodes are among the major and prevalent parasites in aquaculture causing significant loses to fish farmers through fish mortalities and low incomes due to reduced fish quality. Although management of parasites depend on understanding of the life-cycle, biology, epidemiology and all associated potential hosts, there is limited information on the snail species which are the intermediate hosts to various trematodes in Uganda. Hence, the study investigated the diversity of aquatic snail species and associated digenetic trematode cercariae types. A total of 475 snails were collected from fish ponds, tanks, tank supply and drainage channels, examined and classified into four species: Lymnaea natalensis, Ceratophallus natalensis, Bulinus forskalii, and Pila ovata ovata. Study results revealed that B. forskalii was the most abundant constituting 44.42% due to endemic effect, water stagnation and C. natalensis was the least occurring (9.05%) due to dislodging by flowing water as a result of small size. Furthermore, the occurrence and distribution of snails across sampling sites was attributed to differential composition and distribution of macrophyte since each plant species is fed on by specific gastropods. Upon exposure to sunlight L. natalensis shed Echinostome cercariae with infection prevalence (13.33%, 32/60) while B. forskalii released: Rubenstrema exasperatum, Strigea, Schistosome and Plagiorchis cercariae with an overall infection prevalence (19.17%, 43/100). Plagiorchis cercariae were released in extremely high numbers compared to the rest of cercariae due to multiple development stages undergone by the parasite. The differences in snails harboring cercariae highlights the specialization of the trematodes in snail intermediate hosts. The study revealed a risk of occurrence of snails in transmission of trematodes around aquaculture farms, hence further studies should be conducted to determine the metacercariae and associated pathologies in fish to provide best management programmes of trematode parasites in aquaculture systems in Uganda.