Annual outbreaks of a severe ulcerative disease with high mortalities of wild and pond cultured freshwater fish have been reported throughout South-East Asia since 1980. The condition is characterized by the appearance of large, deep ulcers on the body and/or head with varying degrees of destruction of the underlying tissues. Many species are considered to be susceptible but the striped snakehead (Ophicephalus slriants), one of the economically most important species has perhaps suffered the most severe losses. Pollution of the natural waterways and fish ponds with insecticides and herbicides, particularly paraquat, is believed by some workers to be the major cause of disease whereas others consider nature. distribution and pattern of spread of the outbreaks to be more consistent with an infective condition.