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The study examined the acute toxicity of Chlorpyrifos 40EC, a soluble pesticide, on Clarias gariepinus fingerlings under laboratory conditions using static non-renewable bioassays for 96hrs. The fish (weight 0.6- 0.8 kg) were exposed to four different concentrations of 0.4 ml/l, 0.8 ml/l, 1.2 ml/l, 1.6 ml/l, and 0.0 ml/l as control. The physicochemical parameters of the test media were relatively stable except for the total dissolved solids (TDS) and conductivity, which increased with increased concentration and exposure time. The LC50 of Chlorpyrifos 40 EC was observed at 0.76 ml/l while the LT50 was found to be 0.4mg/l, 0.8mg/l, 1.2mg/l and 1.6mg/l for 120.22hrs, 95.50hrs, 66.07hrs, and 36.08hrs respectively. The ANOVA revealed significant variation between treatments and control for fish mortality (P<0.05). The physiological changes analyzed revealed that Tail Beat Frequency (TBF) decreased while the Opercula Beat Frequency (OBF) increased with an increase in concentration and exposure time. The fish exposed to the extract displayed behavioral changes like prolonged vertical movement, rapid movement, jumping, and changes in skin colour with the heavy secretion of mucus. This study shows that Chlorpyrifos is toxic to fish, which implies that stringent measures should be taken to ensure the restraint of its usage by the local fishers to reduce the potential risk of poisonous fish consumption and pollution of the aquatic ecosystem.