Comparative evaluation of the acute toxicity and behavioural changes inClarias gariepinusfollowing exposure to dichlorvos and primextra pesticides

Dichlorvos is an organophosphate pesticide used for the control of pests in crops and stored products, while primextra is a commercial herbicide formulation generally used in agriculture for weed control. The present study was designed to evaluate and compare the acute toxicity of dichlorvos and primextra pesticides and assess their effects on mortality and behavioural changes of Clarias gariepinus juveniles. The 24, 48, 72 and 96 h LC50 of dichlorvos were 6.06, 4.96, 1.65 and 1.29 mg l−1, while those of primextra were 9.34, 6.50, 5.41 and 4.67 mg l−1, respectively. The safe levels estimated by different methods varied from 1.29 × 10−1 to 1.29 × 10−5 mg l−1 in dichlorvos and from 4.67 × 10−1 to 4.67 × 10−5 mg l−1 in primextra. Behavioural changes, such as hyperactivity, gulping of air, skin discoloration, loss of balance, convulsion, erratic swimming and mucous secretions, were observed in fish exposed to both pesticides. Our study indicated that dichlorvos (96 h LC50 = 1.29 mg l−1) was more toxic to C. gariepinus compared with primextra (96 h LC50 = 4.67 mg l−1). The use of these pesticides in both terrestrial ecosystems and aquatic environments should be subject to strict control and monitoring to prevent potential ecotoxicological hazards to aquatic lives.