Keywords: 
• Zn²⁺ /
• Bufo gargarizans /
• tadpoles /
• growth /
• development

Abstract: Zinc (Zn) is one of the most toxic heavy metals and affects a wide spectrum of organisms. Its natural occurrence in the environment is rather low, but it is significantly increased by anthropogenic inputs, such as agricultural and industrial applications. From an ecotoxicological point of view, amphibians are useful indicators of freshwater contamination. The purpose of this study is to assess the toxic effects of zinc ion (Zn²⁺) on the larvae of B. gargarizans. Tadpoles were exposed to zinc (0, 10, 50, 100 and 500 μg·L^-1 Zn²⁺) from the beginning of larval period (G26) through metamorphic climax (G42). Firstly, total length, body length, body weight, and developmental stage of tadpoles were determined on day 15 and 30 after Zn²⁺ exposure. Secondly, metamorphosis and body size (total length, body length, body weight, and hind limb length) at metamorphic climax (G42) were examined. Finally, skeletal systems of tadpoles at G42 were investigated by using double staining methodology. Our results showed that Zn²⁺ at 500 μg·L^-1 could inhibit tadpole growth and development on day 30 after Zn²⁺ exposure. In addition, there was a significant decline in percentage of tadpoles reaching metamorphosis climax, especially for larvae exposed to 500 μg·L^-1 Zn²⁺. Moreover, significant reduction in tadpole size (total length, body length, and hind limb length) at G42 and deposition of calcium were observed at 500 μg·L^-1 Zn²⁺. These results suggested that high dose exposure to Zn²⁺ could inhibit growth and metamorphosis of B. gargarizans. On the basis of these results, more attention should be paid to the potential impact of Zn²⁺ on amphibian health in future.