Author(s): Ganesh Bahadur Thapa, Joydeb Pal

Abstract: EUS/MG/RSD/UM/EGA has been considered the most serious disease of fish and caused heavy loss since its initial outbreaks (February 1989) generally occurring during November to March in Nepal. Three fish farms - Baidya Tankisinwari, Babia Birta and Tarahara were selected as disease prone areas of Eastern Nepal. Water analysis was conducted monthly for two years (November 2008 to October 2010). Histological slides were prepared from infected fish tissues and stained with H E, GMS and PAS observed by microscope. Smear of slightly ulcerated tissue was stained with cotton blue for fungi. This work evaluates the prevalence of epizootics, predisposing environmental factors, route of causative agent into fishes and biosecurity. High fluctuation of water temperature, low pH, DO, decreasing TA and TH suppress the immunity of fishes and easily attacked by A. invadans from contaminated water outbreak the EUS. In Tarahara pond though the condition was almost similar but EUS did not appear which clearly showed that such condition may not always develop the EUS. Among collecteted fishes about 60% Cirrhina mrigala 30% Labeo bata/L. rohita,10% Channa sp., Puntius sp., Mystus sp., Catla catla and Heteropneustes fossilis were EUS affected in which pinhead-sized, red spots on the body surface, head and fin, caudal peduncle, operculum with no visible ulcers but acute dermatitis forming rosacea ultimately the muscle ulcers became deep and necrotic. Histological slides revealed granulomatous, Aphanomyces filaments in muscle, vacuolation, necrosis in the liver and kidney led to death. Farmers reduce the risk of heavy loss from EUS by adopting treatment and preventive measure.

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