Chlorpyrifos is a widely used organosphosphate insecticide in India. Residue of the insecticide is frequently detected in trace to moderate concentration in food grains and in surface water of different freshwater ecosystems of the country. In this study, 96 h LC50 of the technical grade (94% a.i.) and commercial formulation (20% EC) of chlorpyrifos to freshwater fish Oreochromis niloticus were determined as 90.0 and 42.0 µg/L based on 2 h actual concentration of chlorpyrifos in water. About 96 h exposure to sublethal concentrations (0, 12.0 and 25.0 μg/L) of the commercial formulation (20% EC) of chlorpyrifos reduced the level of hepatic glycogen, activities of alkaline phosphatase, acetylcholinesterase, and catalase in liver and elevated the level of plasma glucose and activities of hepatic acid phosphatase, aspartate aminotransferase, and alanine aminotransferase in O. niloticus. About 28-day exposure to these sub-lethal concentrations caused anemia in fish, while 90 days exposure reduced growth of the fish and carcass concentration of crude protein and crude lipid as compared to control. It was concluded from this study that commercial formulation of chlorpyrifos (20% EC) was highly toxic to O. niloticus. Exposure to sub-lethal concentrations of the insecticide could induce oxidative stress and anemia resulting in reduced growth of the fish.
Keywords: Chlorpyrifos; LC; enzymes; growth; plasma; protein.