| The larval stage is an important period in amphibian, which is sensitive to the environmental change and chemical pollution. To study the effect of cadmium on the development of larval in amphibian, the process on growth and development in stage 26~27 R. chensinensis and stage 37~38 R. nigromaculata larval treated with cadmium was observed, the metamorphosis time was noted. The gonads in heteromorphy R. chensinensis and R. nigromaculata were anatomized, female and male were differentiated, and rand atio in sex and malformation were calculated. The localization of the estrogen receptors (ER), FOS and metallothionein (MT) was studied by immunocytochemistry on the liver of young R. chensinensis and R. nigromaculata frogs, relationships among ER, c-fos, MT and cadmium are revealed, and the hormone effect and toxicity in cadmium are also discussed. The main conclusion in this paper is:1. Acute toxicity of cadmium to tadpole R. chensinensis in tap water and deionist water is studied, 0% lethal concentration (LCo), 50% lethal concentration (LC50), 100% lethal concentration (LC100) and the safe concentration (SC) at 24, 48, 72 and 96 hour is calculated. The results showed that in tap water, the LC0, LC50, LC100 of cadmium at 24 hour is 3.16, 5.72, 8.71mg/L; At 48 hour is 2.64, 5.14, 8.25 mg/L respectively; at 72 hour is 2.64, 5.14, 8.25mg/L respectively; and at 96 hour is 2.04, 3.10, 4.96mg/L respectively; SC is 1.22mg/L. In deionist water, the LCo, LC50 and LC100 of cadmium at 24 hour is 0.10, 0.16, 0.22mg/L; at 48 hour is 0.10, 0.15, 0.21 mg/L respectively; at 72 hour is 0.09, 0.13, 0.15mg/L respectively; and at 96 hour is 0.09, 0.12, 0.16mg/L respectively; SC is 0.04mg/L. The results show that the death rates of tadpoles is increasing with the concentration and time up, the toxicity of deionist water with cadmium is higher than that of tap water with cadmium.2. The heteromorphic time in stage 26~27 R. chensinensis and stage 37~38 R. nigromaculata larval is calculated, in the groups of 0, 0.05, 0.1, 0.2 and 0.4mg/L cadmium in 90% tadpoles R. chensinensis, the heteromorphic time is 66.4±1.9, 78.3 ± 2.9, 90.3 ± 3.9, 105.6 ± 8.6 and 141.6±4.1 days respectively. The difference between control and treatment groups is obvious (P<0.05). The heteromorphic time in the groups of 0, 0.05, 0.1, 0.2 and 0.4mg/L cadmium in 90% tadpoles R. nigromaculata is 41.1 ± 5.3. 40.8 ± 4.6 and 40.3 ± 6.4d respectively, the difference between control and groups 0,0.05, and 0.1 is not obvious (P>0.05), but the heteromorphic time of 0.2 and 0.4mg/L are 49.9 ± 7.4 and 72.8 ±7.5d respectively, contrasted with control group, the difference is obvious (P<0.05). The results showed that with the concentration of cadmium increasing, the growth and development in tadpoles was restrained obviously, the heteromorphic time became longer, growth and metamorphosis in tadpole could be delayed and disturbed.3. The heteromorphic R. chensinensis and R. nigromaculata in different treatment groups were anatomized and the female and male number was calculated, the result is that contrasted with the control group in R. chensinensis, the female and male ratio increase in 0.05mg/L group, the female and male ratio decrease in 0.1, 0.2 and 0.4mg/L groups. In R. nigromaculata, contrasted with control group, the female and male ratio of 0.05 and 0.4mg/L group is not obvious (P>0.05), 0.1 and 0.2mg/L, the female and male ratio descends, the difference is obvious to control group (P<0.05), which shows that the sex ratio in R. chensinensis and R. nigromaculata was affected. The gonads of young R. chensinensis in the high cadmium groups appeared abnormal. The results showed that cadmium might affect the gonad differentiation.4. Limb malformation could be induced by different concentration of cadmium in stage 26~27 R. chensinensis. The tail in tadpole was curved; the front and back limbs were curved and malformed in the young frogs, which were caused mainly by the malformed joints. The results show that early process of limbs in tadpole R. chensinensis could be disturbed by cadmium. The limbs were not affected by cadmium in stage 37~38 R. nigromaculata, which showed that the process of limb development was not affected by cadmium in this stage.5. After metamorphism was finished in 0.05, 0.1 and 0.2mg/L group in R. chensinensis and R. nigromaculata, effect of cadmium on the tadpoles was stopped in 0.4mg/L groups. After 36d ± 4.1 d, the metamorphism in 90% R. chensinensis was finished, and after 90% 23d ± 7.5 d, the metamorphosis was finished in R. nigromaculata. The results show that after the effect of cadmium on R. chensinensis and R. nigromaculata was stopped, the repression on the growth was reversed, the growth in tadpoles retrieved.6. The ER masculine grains located on the liver in the controlled and treated groups in male young R. chensinensis and R. nigromaculata. In the 0.05mg/L group, ER expressed strong masculine, in 0.1 and 0.2mg/L group, ER expressed weak masculine.
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