In order to study the acute toxicity of three kinds of ions (Cu²⁺, Zn²⁺, Al³⁺) on loach and the change of the processed loach liver antioxidant enzyme activity and lipid peroxidation, experiments have been conducted. The result shows that for loach exposed to Cu²⁺, Zn²⁺, Al³⁺ solutions, the 24 h half-lethal concentrations are Zn²⁺ 3.243 and Al³⁺ 1.497 mg/L; the 48h half-lethal concentrations are Cu²⁺1.054 mg/L, Zn²⁺3.017 mg/L and Al³⁺ 1.425 mg/L; the 72 h half-lethal concentrations are Cu²⁺ 0.666, Zn²⁺3.017 and Al³⁺ 1.386 mg/L; the 96 h halflethal concentrations are Cu²⁺ 0.563 mg/L, Zn²⁺ 2.874 mg/L and Al³⁺ 1.350 mg/L. The 96 h safe concentrations are Cu²⁺0.563 mg/L, Zn²⁺ 2.874 mg/L, and Al³⁺ 1.350 mg/L. Thus, the order of toxicity to loach from strong to weak is Cu²⁺>Al³⁺>Zn²⁺. For loach exposed to a Cu²⁺-Zn²⁺-Al³⁺ mixed solution, the 48 h, 72 h, the 96 h joint toxicity effect performances are respectively antagonistic action, antagonistic action, and synergy. The safe Zn²⁺ concentration of loach is 0.029 mg/L, which is far lower than 0.10 mg/L, the National Standard of Fishery Water Quality in China.

Cu²⁺  /  Al³⁺  /  Zn²⁺  /  loach  /  single toxicity  /  joint toxicity