Aquatic toxicity risks of agricultural pesticides to non-target organisms especially fishes are pivotal. These pesticides influence metabolism at very low concentrations by disrupting physiological balances. An attempt has been made in the present investigation to determine the acute toxicity of chlorpyrifos on oxygen consumption and food consumption of freshwater fish, Oreochromis mossambicus (Peters). Shortterm acute toxicity tests were performed adopting renewal bioassay technique over a period of 96 hr, using different concentrations of chlorpyrifos to the fish and the 96 hr LC50 value was found to be 0.022ppm. For oxygen consumption and food consumption study, the fish were exposed to two sublethal concentrations viz., 1/5th of LC50 (0.0044 ppm) and 1/10th of LC50 (0.0022 ppm) along with lethal concentration (0.022 ppm) as reference for 48 hr indicated that lethal concentrations had profound effect than sublethal concentrations. The fish exhibited respiratory distress (such as gasping in air), loss of balance and erratic swimming prior to death. Chlorpyrifos had a significant effect on functional activity of experimental fish by altering respiration rate and impairing feeding behavior.
