Inhibitory effect of cadmium exposure on digestive activity, antioxidant capacity and immune defense in the intestine of yellow catfish (Pelteobagrus fulvidraco).

Cadmium (Cd) is a toxic heavy metal that can pose a serious threat to aquatic organisms. To evaluate the physiological response and defense mechanism of fish intestine to Cd toxicity, yellow catfish (Pelteobagrus fulvidraco) were exposed to 0 (control), 50 μg/L and 200 μg/L Cd2+ for a period of 8 weeks, and then histological changes, digestive activity, antioxidant status and immune responses in the anterior intestine were assessed. After exposure, significant growth retardation and Cd accumulation were observed, and obvious histopathological lesions in the intestine such as increased goblet cells, excessive mucus, vacuolization and thickened lamina propria were detected. Intestinal digestive enzymes activities and related gene expression were inhibited markedly in Cd2+ treatments. Furthermore, Cd exposure induced oxidative stress inhibiting antioxidant activity, characterized by an increase in malondialdehyde level as well as the decrease in the activity and transcription level of antioxidant enzymes. In addition, exposure to Cd2+ down-regulated the expression of key genes involved in the immune response (lys, c3, tor, tgf-β, il-10, tnf-α and il-8), suggesting immune defense was inhibited. Taken together, the decreased digestive enzyme activity and Cd-induced toxicity stress for antioxidant and immune systems in the intestine might be account for individual growth retardation.