Abstract: Xenopus laevis tadpoles (NF51) were exposed to cadmium chloride at the concentrations of 0.01, 0.1and 1 mg·L^-1Cd²⁺ for 21 days. The changes of growth, metamorphosis and thyroid gland of X. laevis were observed. Compared with the control, the body weight (BW), snout to vent length (SVL) and hind limb length (HLL) were decreased by 0.39, 0.17 and 0.27 fold in 1 mg·L^-1Cd²⁺treatment group after exposure for 7 days, respectively. The hind limb length (HLL) was decreased by 0.11 fold and the development showed one stage slower in 1 mg·L^-1 treatment group after exposure for 21 days. And the other treatment groups did not show significant changes in BW, SVL, HLL or development stages after exposure for 7 and 21 days. Cadmium chloride treatment decreased the number of follicle, and induced the depletion of colloid and even vacuolation after exposure for 21 days. In addition, amalgamation of two or more follicles occurred in 1 mg·L^-1 treatment group. Our results suggested that cadmium chloride had thyroid hormone disrupting effects and might disturb thyroid gland tissue directly. Therefore, AMA was further proved to be a valid tool to screen the thyroid hormone disrupting effect of heavy metal salt.

Key words: Xenopus laevis, cadmium, metamorphosis, thyroid disrupting chemicals (TDCs), Xenopus laevis, cadmium, metamorphosis