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Journal of Fisheries and Aquatic Science

Year: 2023 | Volume: 18 | Issue: 1 | Page No.: 5-9
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Authors

G.A. Oladosu

G.A. Oladosu

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Research Article

Severe Metacercarial Invasion of the Gills of Farmed Clariid Catfish Juveniles

G.A. Oladosu G.A. Oladosu's LiveDNA
Background and Objective: Mass mortality of earthen-pond reared Clarias gariepinus and hybrid catfish juveniles were reported to the Veterinary Teaching Hospital of the University of Ibadan, Nigeria. The incidence of the disease condition, especially with the presence of aquatic snails in the culture facility that is stream-fed necessitated clinicopathological and epizootiological investigations to determine the causal factor and the course of the disease. Materials and Methods: Five samples of each clariid catfish species were clinically examined, sacrificed and dissected for autopsy. Microscopy of gill tissue, skin, and intestinal scrapings, as well as crush preparations of the liver, the kidney and the eye lens, was conducted. Also, 5 aquatic snail samples were cracked open and snail tissues were subjected to microscopy. Experimental infection was conducted by making 10 healthy catfish juveniles cohabit with 20 infected snails. Results: Numerous cysts were observed in the gills of the fish samples submitted for clinical examination, with severely disrupted structures. Microscopy of the snails revealed the presence of numerous cercaria, and that of the gills revealed the presence of cysts identified to be metacercaria of a digenea trematode. Experimental infection confirmed transmission of the trematode from snail to fish. Mass fish mortality reported was occasioned by decreased respiratory tolerance due to severe gill damage caused by the invasion of the digenea metacercaria. Conclusion: The aquatic snail observed in the affected ponds is the first intermediate host of the worm. Aquatic snails should therefore be eliminated from ponds as part of routine pond preparation to reduce the risk of digenea infection and possible zoonosis.
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