Duration of Induced Metallothionein is a Critical Factor in the Cadmium-Resistance Among Goldfish (Carassius auratus) and Common Carp (Cyprinus carpio).

According to the Environmental Protection Agency in Taiwan, the common carp (Cyprinus carpio) is one species of fish for acute toxic test. It has been found to be extremely sensitive to the toxicity of Cd2+; Furthermore, the goldfish (Carassius auratus) has a higher resistance than common carp upon Cd2+ exposure, but both fish are the same family. The aim of the study was to compare the physiological and histo-pathological responses between goldfish and common carp under exposure to sublethal concentrations of Cd2+ in order to understand the reasons behind the Cd2+-resistance. Results showed that metallothionein (MT) protein levels in visceral tissues were exceptionally increased and elevated at an earlier time in goldfish than in common carp. Meanwhile, the amount of Cd2+ accumulation in goldfish was higher than common carp after Cd2+ exposure. The histo-pathological results revealed that the density of gill mucus cells and the thickness of gill epithelium in common carp were raised earlier than in goldfish, but the histo-pathological findings resemble each other. According to the data, we suggested the efficient response of MT proteins may contribute to goldfish with a higher Cd2+ tolerance.