10.22376/ijpbs.2019.10.1.p1-12 Volume 1 Issue 4 2010 (October - December) Static renewal evaluation of the acute toxicity of an organophosphate pesticide, dimethoate against the freshwater fish lessThan i greaterThan H. fossilis lessThan /i greaterThan was conducted in the laboratory. lessThan i greaterThan H. fossilis lessThan /i greaterThan showed behavioural changes against dimethoate intoxication. There were increased opercular movement, sluggish, lethargic and abnormal swimming, loss of buoyancy and muscular tetany. The treated fishes also showed fading of their body colour. The LC lessThan sub greaterThan 50 lessThan /sub greaterThan values of dimethoate to the freshwater catfish, lessThan i greaterThan Heteropneustes fossilis lessThan /i greaterThan at various exposure periods are 15.92 mg/l for 24 h; 13.42 mg/l for 48 h; 12.39 mg/l for 72 h and 11.34 mg/l for 96 h. The upper confidence limits were 16.59, 14.72, 13.54 and 12.86 mg/l for 24, 48, 72 and 96 h and lower confidence limits were 15.32, 12.18, 11.23 and 9.79 mg/l, respectively. From the present study it seems that the freshwater catfish, lessThan i greaterThan H. fossilis lessThan /i greaterThan is more susceptible to dimethoate toxicity as the LC lessThan sub greaterThan 50 lessThan /sub greaterThan value for this organophosphate is less than other reported fish species. These results indicate that dimethoate exposure to the fish caused toxic effects. Anoop Kumar Srivastava,Diwakar Mishra,Shilpee Shrivastava,Sunil Kumar Srivastav,Ajai K. Srivastav LC50, dimethoate, fish, toxicity, organophosphate 359-363