Ecophysiological Effects of Waterborne Zinc on Ctenopharyngodon idellus

The juvenile Ctenopharyngodon idellus (19.68±0.17 g) were exposed to the solutions of zinc sulfate heptahydrate (ZnSO4.7H2O), to observe the toxic effects of waterborne Zn on this fish. The results showed that the median lethal concentration (LC50) over 96 h of waterborne Zn2+ was 5.00 mg/L. After 8 weeks of chronic exposure, the final weight and the specific weight growth rate of C. idellus decreased with the increasing Zn2+ concentration, and the differences were significant among the three groups (P < 0.05). The content of ash in the high exposure group was significantly higher than those in the other two groups (P < 0.05). The dry mass in the two exposure groups and the energy density in the low concentration group were significantly higher than those in the control group (P < 0.05). The contents of Zn in the hepatopancreas, gill, intestine, muscle, and whole body in the high concentration group were significantly higher than those in the control group (P < 0.05). The contents of Zn in hepatopancreas were significantly higher than those in other organs (P < 0.05). There was no significant difference for the contents of Zn in the intestine and gill in the two Zn exposure groups, but those were significantly higher than those in other organs except hepatopancreas (P < 0.05). The content of Zn in muscle was significantly lower than that in the other organs. It suggests that the pattern of energy allocation of the C. idellus is changed by the Zn exposure. Fat was preferentially used to provide extra energy for the detoxification under the Zn exposure, and the rates of the protein and energy deposited in the body were reduced. Therefore, the growth of the fish was depressed. The C. idellus mainly takes up Zn through the gill and distributes Zn to other tissues via blood circulation.