Abstract: The effects of different concentrations (0.01, 0.1, 2.0 and 5.0 mg·L^-1) of La³⁺ on the antioxidant activity and esterase (EST) isozymes in kidney and gill ofCyprinus carpio Linnaeus were studied by renewal test. The results indicated that within the test concentration range of LaCl₃ and after treated for 4 months, the SOD activities in C. carpio gill was inhibited significantly, while the SOD activity in kidney and the LPO content in gill had no significant differences with the control. The kidney’s LPO content at 0.01, 0.1 and 5.0 mg·L^-1 of La³⁺ had no significant difference with the control, butwas much higher at 2.0 mg·L^-1 of La³⁺. The POD activities in kidney and gill at 0.01 and 0.1 mg·L^-1 of La³⁺ were significantly higher than the control, but were inhibited significantly at 5.0 mg·L^-1 of La³⁺. PAGE test showed that under effects of La³⁺, the band lightness of SOD and EST in kidney and gill changed distinctly, several bands of EST isozymes in kidney and gill disappeared, and some new bands of EST isozymes in kidney were observed. These effects varied with different La³⁺ concentrations.

Key words: Taihu Region, Nitrogen wet deposition, Seasonal dynamics, Ecological significance