Salmonid fish and flounders are economically important fish cultured in northern Japan. Viral diseases remain one of the limitations to the successful propagation in aquaculture. The incidence of disease, especially viral disease, has been increasing. Methods currently used to control viral disease in hatcheries are: (a) hygiene and sanitation, (b) disinfection of water supplies and wastewater, (c) selection of pathogen- free broodstock, (d) health monitoring of hatched fry, (e) control of normal intestinal flora, (f) vaccination, and (g) temperature control
