Adverse effects of cadmium exposure on the immune and antioxidant system functions of dongtingking crucian carp (Carassius auratus indigentiaus)

Cadmium (Cd) is one of the main pollutants in the water environment, exhibiting bioaccumulation and toxicological effects on fish. In this study, dongtingking crucian carp (Carassius auratus indigentiaus) were exposed to 0 (control group), 0.1, 0.5 and 1.0 mg/L Cd for 30 days. The results showed that the liver body index and spleen body index increased gradually with increases in the Cd concentration, and morphological changes were observed in the spleen and liver. The level of accumulation of Cd in the tissues was as follows: gut > middle kidney > liver > spleen > gills > heart > brain > muscles. With increases in the concentration, the Cd enrichment concentration increased gradually in the spleen and middle kidney. Pathological features were observed in the intestines, gills, spleen and liver of C. auratus indigentiaus after 1.0 mg/L Cd exposure. The Lys content and the AKP, ACP, CAT, GSH-PX and SOD activities were significantly increased in the low concentration Cd exposure group (0.1 mg/L), and dramatically decreased in the high concentration Cd exposure group (1.0 mg/L). The expression levels of the IL-6 and IL-1 beta genes in the intestines, gills, spleen and liver, TNF-alpha gene expression in the gills, spleen and liver, IgM, IgZ and C3 genes expression in the liver decreased gradually with increases in the Cd concentration, while the expression of TNF-alpha gene in intestine, IgM, IgZ and C3 genes expression in intestine and gill increased with increasing Cd concentration. The expression of IgM, IgZ and C3 genes in the spleen were significantly increased in the 0.1 mg/L Cd exposure group, but significantly decreased in the 0.5 mg/L and 1.0 mg/L Cd exposure groups. These results indicate that low concentration of Cd (0.1 mg/L) might induce toxic excitability, but higher concentration of Cd (1.0 mg/L) inhibit the antioxidant and immune systems.