摘要
Heavy metals pose a potential threat to aquatic organisms. In this study, a static-renewal acute toxicity test was conducted to investigate the effects of cadmium on the antioxidant defense systems （both enzymatic and non-enzymatic） and lipid peroxidaton in liver and gill tissues of juvenile GIFT tilapia Oreochromis niloticus. After 8 days of exposure to Cd （0, 0.016, 0.08, 0.4 and 2 mg/L）, livers accumulated significantly more Cd than gills. Catalase （CAT）, superoxide dismutase （SOD） and glutathione S-transferase （GST） activities were stimulated only at the highest concentration tested （2 mg/L）. Glutathione peroxidase （GPx） activity was stimulated in the gill while inhibited in the liver, these alternations in gill and liver showed a strong relationship with Cd levels in these tissues. This may indicate either a tissue-specific response of GPx to Cd or, most probably, a hormetic effect of Cd on GPx. Cd increased GSH levels and decreased the ratio GSSG/GSH in fish livers at 2 mg/L. Cd exposure resulted in an elevated level of MDA in the livers of fish at 2 mg/L, indicating that Cd caused lipid peroxidation. Taken together, the results demonstrated that Cd altered the enzymatic and non-enzymatic defensive systems and caused lipid peroxidation in O. niloticus at relatively high concentrations （compared to environmentally relevant concentrations）. In addition, the results implied that O. niloticus could tolerate high level of Cd in sites polluted by Cd.
