Escalating pesticide deposition in the aquatic environment is becoming a potential threat to aquatic organisms. Present study was designed to investigate acute toxicity in O. niloticus. the fish were exposed to five different concentrations of malathion, chlorpyrifos and lambda-cyhalothrin (synthetic pyrethroid) pesticides in the laboratory using separate aquaria for each chemical. Mortality ranged from 100 to 0%. The 24 h LC50 (median lethal concentration) for O. niloticus was 5.70, 0.5 and 0.015 ppm for malathion, chlorpyrifos and Lambda-cyhalothrin, respectively. LC50 values obtained after 24 h of exposure indicated that the fish were sensitive to all the three tested pesticides. The mortality rate was directly proportional to the pesticides concentration. The results showed that the lambda- cyhalothrin was found more toxic followed by chlorpyrifos and malathion. The study results suggested that the runoff of organophosphates and synthetic pyrethorid pesticides from nearby agricultural fields to aquatic environment posed health hazards on fish.

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