Immunological effects of paraquat on common carp, Cyprinus carpio L

Paraquat (PQ) is a nonselective worldwide used herbicide and it has been demonstrated to be highly toxic to animals and humans. However, relatively little is known about PQ effect on the immune system and histopathology of fish. In the present study, we aimed to determine the lysozyme activities, content of IgM, and complement C3 content in the liver, kidney, and spleen of common carp exposed to 1.596 or 3.192 mg/L of PQ for 7 d. The results showed that lysozyme activity in the liver, kidney, or spleen of common carp was increased at the earlier stages of PQ-exposure (from 1 to 3 d) while decreased at the end of treatment. Moreover, PQ-exposure caused irregular change of IgM content while decreased C3 content. These results suggest that PQ-exposure may disturb the innate immunity of common carp and could result in dysfunction of the specific immunity in common carp. In addition, PQ-exposure also caused remarkable histopathological damages in fish gill, fin, liver, spleen, kidney, and intestine, indicating that PQ has immunotoxicity on common carp.