Effects of water-soluble fractions of diesel oil on the antioxidant defenses of the goldfish, Carassius auratus

Larval goldfish Carassius auratus were exposed to 0.05 and 0.1 mg/L No. 20 diesel oil, widely used as transportation power in China, for 2, 4, 7, 10, 15, 25, and 40 days, while one control group was designated for each exposure group. Some fish after 25 days of exposure were transferred to diluted water until the 40th day. Hepatic antioxidant defense parameters of fish, including contents of reduced glutathione and glutathione disulfide and activities of superoxide dismutase, catalase, glutathione reductase, selenium-dependent glutathione peroxidase, and glutathione S-transferase, were determined and compared to control values. All the results indicated that the antioxidant responses of the fish to the two concentrations of oil exposure were similar on the whole. The possible defense mechanisms of fish and prospective early biomarkers for the evaluation of an oil-dominant contaminated aquatic ecosystem are discussed. In addition, after fish were removed from oil exposure, the recovery status of these antioxidant indices was explored.