We evaluated the acute toxicity of chlorpyrifos (CPF) to juvenile were exposed to 0, 0.18, 0.36, 0.57, 0.86, and 1.1 mg/L CPF in a static test. We measured SOD, CAT activity, and GSH content in liver. CPF was highly toxic with 24, 48, and 96 h LC₅₀ values of (0.296±0.019), (0.16±0.036), and (0.052±0.003) mg/L, respectively. The maximum safe concentration was (0.014±0.003 1) mg/L. The CPF LC₅₀ decreased significantly with time and fit a hyperbolic decay model with a high . CAT activity did not change significantly at low CPF concentrations. Both sampling time and CPF concentration had a significant effect on CAT (<0.05). The concentration of CPF had little effect on GSH content. There was a significant change in GSH levels over time (<0.01). GSH levels declined after 24 and 48 h in the group administrated with 0.36 mg/L CPF but were higher after 96 h. Our results suggest that the toxic effects of CPF can be evaluated by measuring liver CAT and SOD activity and GSH content. Exposure to CPF caused significant damage to the gill and liver, characterized by gill disorder, epithelial cell proliferation, hypertrophy, and blood congestion. Furthermore the liver endothelial cells swelled and merged with one another, resulting in roughness and abnormality of the liver duct wall. Our results can be used to guide development of protocols for the safe use of CPF and the development of eco-friendly farming techniques for .