Seasonal Variation of Diseases of Some Small Indigenous Fishes from Oxbow Lake Fisheries of Bangladesh

Disease investigation through clinical and histopathological observation of three small indigenous fishes Channa punctatus, Puntius ticto and Nandus nandus were carried out from Shidlong Oxbow Lake and Gangni Oxbow Lake of Mymensingh area during April 2000 to January 2001. Fish sampling were monitored on monthly basis. It was observed that most of the fishes of Shidlong Oxbow Lake were more affected than Gangni Oxbow Lake. It was also observed that, all the fishes were more or less normal in their appearance during the month of April to September in both Oxbow Lakes. But severity of infection and injury were increased in October to January. Scale loss, discoloration of gill filaments, red spot in ventral region, weak body, loss of caudal fin and several necrotic lesions on head region were found in C. punctatus in October to January from both Oxbow Lakes. Discoloration of gill filament, rough skin and mild dermal lesions were observed in N. nandus from both Oxbow Lakes in October to January. In P. ticto red spot in ventral region, weak body and hemorrhage in skin and gill were found in October to January. Common histopathological changes include necrosis, pyknosis, inflammation, hemorrhage, hypertrophy and hyperplasia and missing of primary and secondary gill lamella were observed. Monogenetic trematode and protozoan cysts were found in gill filaments of all the three fish species. Many fungal granuloma were observed in the skin and muscle of all the fish species during December to January in both Oxbow Lakes. From the results we can conclude that fishes were affected by Epizootic Ulcerative Syndrome (EUS) and myxoboliasis. It was found that most of the fishes of Shidlong Oxbow Lake were more affected as compared to Gangni Oxbow Lake. Among fish species, C. punctatus was found more affected than other fish and less affected one was N. nandus. Fishes of both selected Oxbow Lakes were severely affected during the month of December and January. However, diseases like trichodiniasis, myxoboliasis, dactylogyrosis, gyrodactylosis and EUS were observed in the sampled fish species.