Effects of Cadmium on Metamorphism and Gonad Differentiation in Rana chensinensis

200 tadpoles Rana chensinensis at stage 26-27 were exposed to 0.05, 0.1, 0.2 or 0.4 mg/L Cd²⁺ in tap water respectively. The heteromorphic young frogs in different treatments were anatomized, females and males were identified through gonad observation, and the female rate was calculated. Localization of estrogen receptors (ER) in liver cells was investigated in different treatments by using immunocytochemistry. The results showed that Cd²⁺ might induce limb abnormality. There was little correlation between abnormality rate and cadmium concentration in lower Cd²⁺ levels; however, limb abnormality ratio was higher in the 0.4 mg/L group. On the other hand, Cd²⁺ could affect gonad differentiation. Compared to the control group, the proportion of female population increased in the 0.05 mg/L group and decreased in the 0.1, 0.2 and 0.4 mg/L ones. The sex rate in the 0.2 mg/L group is significantly different from that in the control group. Hermaphrodite gonads were observed in the two treatments with 0.2 mg/L and 0.4 mg/L of Cd²⁺. Additional, ER expression was positive in both cytoplasm and nucleolus of liver cells in Cd²⁺ treated groups. But, there was no linear relationship between ER expressions levels and the concentration of Cd²⁺. These results suggested that cadmium could influence tadpole metamorphosis and gonad development by affecting the secretion of sex hormone.