Almost all the pesticides and more particularly the synthetic pesticides used, find there way into water bodies alter themetabolism of aquatic organisms is known long back. In the present investigation, the effect of sub lethalconcentration of chlorpyrifos toxicity on fish Channa punctatus were studied after 24hrs, 48hrs, 72hrs and 96hrsexposure respectively. Chlorpyrifos is an organophosphate insecticide that kills insects by disrupting there nervoussystem and is effective against a wide range of plant eating insects. Suspected effects of chlorpyrifos exposureinclude birth defects, increased rate of leukemia and immune system abnormalities. The results indicated a significantincrease in ESR (mm/hr) 2.57mm/hr, 2.60mm/hr, 2.71mm/hr and 2.83mm/hr when compared to control group2.56mm/hr fallowing both acute and sub acute exposure of chlorpyrifos.