The side-effect of Azadirachta indica (A. Juss) on certain enzyme activities of a freshwater catfish, Heteropneustes fossilis was studied for a period of 24,48,72,and 96 hr, at sub lethal concentration. During the exposure period the alkaline phosphates and acid phosphates content in the liver, muscle and intestine of treated fish showed decreasing trend. The alterations of these biochemical parameters can be effectively used as nonspecific biomarkers against plant extract toxicity stress and also help safer usage of plant extracts in aquaculturefarms.