Health Condition of a Farmed Tilapia (Oreochromis niloticus) in Earthen Ponds, Northern Bangladesh

Investigation on health conditions of a farmed tilapia (Oreochromis niloticus) in two upazilas of Mymensingh District were carried out through clinical and histopathological observation during September, 2010 to March, 2011. Fish sample and water quality parameters (temperature, dissolved oxygen, pH, alkalinity, nitrite and ammonia) were monitored on a monthly basis. Clinical observations of the fish were also done for any kind of abnormalities at monthly intervals. Samples of skin, muscle, liver and kidney were observed by histological techniques. Among the water quality factors, water temperature and alkalinity were found at unfavourable level for fish during the colder months. Clinically, it was observed that the tilapia were more affected from December and January and almost normal in appearance during September, October, November and March. Different clinical symptoms like rough skin, scale loss, red spots and dermal lesions were noticed in December and January. Histopathologically, sampled fish were found almost normal in the months of September and October. In the month of November minor pathologies were found to be started. Marked pathological changes like necrosis, pyknosis, hemorrhage, hypertrophy, hyperplasia, missing of primary and secondary gill lamellae, vacuums, fat droplets and fungal granuloma and fungal hyphae were observed in fish organs during December and January. Whereas, the pathological condition of fish gradually reduced in February. Again when considered individual fish pond, fishes of pond 1 (P1) in Bhaluka upazila were more affected than other ponds. The study showed that severity of clinical and pathological changes were increased in December and January. During the period of Epizootic Ulcerative Syndrome (EUS), bacterial and protozoan diseases were evident.