Toxicity and the effect of sub-lethal concentrations of endosulfan on a fresh water fishBarbus stigma had been studied. Endosulfan proved to be lethal toB. stigma at a concentration of 0·01 ppm and above. The LC50 was 0·0043 ppm and the sub-lethal concentration was 0·003 ppm and below. At sub-lethal concentrations the fish exhibited erratic swimming activity and at lethal concentrations it lost the sense of balance. The rate of feeding was reduced by 5·94% to 9·02% and assimilation by 6·44 to 9·60% in different sub-lethal concentrations. Growth (weight) retarded from 11·6mg/day in the control fish to. 7·3, 6·0 and 5·1 mg/day in the endosulfan treated fishes. Respiratory rate of the pesticide treated fish also dropped by 10 to 16·6%. Due to. the over all effect of the toxicity, the fish,B. stigma comparatively showed a poor nutritive value by displaying a drop of nearly 35% in the organic constituents.