Effects of carotenoids on the growth performance, biochemical parameters, immune responses and disease resistance of yellow catfish (Pelteobagrus fulvidraco) under high-temperature stress

The yellow catfish (Pelteobagrus fulvidraco) is an economically important species in eastern Asia, but its aquaculture faces bottlenecks due to the influence of environmental factors. The present study evaluated the effects of dietary carotenoid supplementation on high-temperature stress and disease resistance in yellow catfish. Fish were randomly assigned to one of six treatments: five groups were fed basal diets supplemented with 50, 100, 150, 200 or 250 mg.kg(-1) carotenoids, and a control group was fed a basal diet. The feeding experiment lasted 60 d, after which the fish were exposed to acute heat shock for 1 d and then infected with Proteus mirabilis. The results showed that the specific growth rate (SGR) and weight gain (WG) were significantly increased and the feed conversion ratio (FCR) was significantly decreased in the groups supplemented with 100, 150, 200 and 250 mg.kg(-1) carotenoids (P < 0.05) compared with the control group. Yellow catfish fed 150-200 mg.kg(-1) carotenoids exhibited significantly increased serum lysozyme activity; increased total protein (TP), thyroxin (T4), immunoglobulin (Ig), complement 3 (C3) and complement 4 (C4) concentrations; increased liver total antioxidant capacity (TAC) and catalase (CAT), and superoxide dismutase (SOD) activity; increased liver hepcidin, immunoglobulin M (IgM), lysozyme G (LysG) and heat shock protein 70 (HSP70) gene expression; and decreased serum aminotransferase (ALT) and liver malondialdehyde (MDA) levels prior to stress exposure (P < 0.05) compared with those in the control group. Additionally, supplementation with 200 mg.kg(-1) carotenoids decreased serum cortisol levels prior to stress exposure. The groups supplemented with 150, 200 and 250 mg.kg(-1) carotenoids also exhibited significantly increased serum lysozyme activity after stress exposure (P < 0.05). Dietary supplementation with 100-250 mg.kg(-1) carotenoids decreased yellow catfish mortality from P. mirabilis infection. These results suggest that supplementing a basal diet with 150-200 mg.kg(-1) carotenoids enhances immune responses to disease and imparts resistance to high-temperature stress in yellow catfish.