Abstract: A laboratory experiment was conducted to study the effects of different concentration (0, 3.2, 5.6, 7.5, 10.0, and 18.0 μg·L^-1) avermectin on the catalase (CAT) and glutathione-S-transferase (GSTs) activities of common carp (Cyprinus carpio). Both the CAT and the GSTs activities in the muscle and liver-pancreas of common carp in all but 3.2 μg·L^-1 dose groups were significantly affected. The enzyme activities were induced when the avermectin concentration was low, but inhibited when the avermectin concentration was high. The CAT activity in the muscle of common carp in 5.6 μg·L^-1 and 7.5 μg·L^-1 dose groups had little difference with the control, but the CAT activity in the liver-pancreas and the GSTs activity in the muscle and liver-pancreas of common carp in 5.6 μg·L^-1 and 7.5 μg·L^-1 dose groups increased significantly, compared with the control. Both the CAT and the GSTs activities in the muscle and liver-pancreas of common carp in 10.0 μg·L^-1 and 18.0 μg·L^-1 dose groups had a significant increase first, and decreased significantly then. When the common carp was transferred to aquaria with no avermectin for 10 days, both the CAT and the GSTs activities in the muscle and liver-pancreas of the common carp in all dose groups except in 18.0 μg·L^-1 dose group were recovered to the levels of the control group, which meant that high concentration avermectin might have an irreversible damage to the fish. There existed dose-effect relationships between the avermectin concentration and the CAT and GSTs activities in the muscle and liver-pancreas of common carp, suggesting that the CAT and GSTs activities in the muscle and liver-pancreas of common carp could be used as the biomarkers to monitor the avermectin pollution of water body. Meanwhile, the CAT and GSTs activities in the liver-pancreas of common carp exposed to avermectin changed much more markedly than those in the muscle, and thus, the liver-pancreas was the better sampling organ when the CAT and GSTs activities were used as the biomarkers.

Key words: Cotton, NH₄⁺, NO₃^-, Nitrogen, Metabolism