Pathological and Biochemical Index Changes in Different Tissues of Cyprinus carpio Exposed to Cadmium

Background: Cadmium (Cd) is among the most toxic metals and is widely distributed in aquatic environments. Objective: Histopathological lesions and biochemical indices can be used to reflect the toxic effects of cadmium in fish target organs. Methods: In the present study, the common carp Cyprinus carpio was exposed to 0.5 mg/L of CdCl2 for 21 days. Histopathological analyses were performed in the spleen, liver, kidney, gills and head kidney tissues of C. carpio, and tissue sections were stained with hematoxylin-eosin (HE) and observed under an optical microscope. The acid phosphatase, alkaline phosphatase, and lysozyme activities were determined. Results: The results showed that there were various pathological changes in five major tissues of C. carpio. The kidney, gills, and liver were the most affected organs during cadmium exposure, and deformation and disorganization of epithelial cells, vacuolization formation, serious hemorrhages and necrosis were also observed. In addition, 0.5 mg/L cadmium exposure significantly increased serum lysozyme and acid phosphatase activities and inhibited alkaline phosphatase activity. The present study showed that cadmium stress causes significant pathological tissue changes and influences lysozyme, acid phosphatase and alkaline phosphatase activities in C. carpio. Acid phosphatase and lysozyme activities are sensitive to cadmium. Conclusion: In conclusion, the toxicity of cadmium caused varying degrees of pathological and biochemical changes in fish tissues in C. carpio.