Environmental pollution is a matter of global concern today . Third world countries had to response to increasing demands for increasing population,proverty,illiteracy,poor sanitation etc together with the pollution related problems. Pesticide applied to food crop in the field can also leave potential harm ful residue. these increasing pesticide residue effect adversely on whole environment, fauna and flora Including man. The toxicological impact of organ phosphorous pesticide Malathion on the general and behavioral aspects. histopathological analysis brain tissue cf the Indian cat fish H Fossilis was investigated. After exposing the fishes in different Malathion concentrations exhibited abnormal behavioural response with various toxic symptoms as indicated by visible changes in various physiological activities, including a marked increase in respiratory activity . Therefore, pesticide monitoring and risk assessment should immediately be undertaken in North Eastern Sates of India and the banned as a agrochemical to conserve the healthy aquatic environment and to promote the natural rhythm of fish production