Dietary Zinc Supplementation Improves Growth, Antioxidant Capacity, Immunity, and Intestinal Health in Juvenile Black Carp (Mylopharyngodon piceus)

Zinc (Zn) is an essential trace element that plays important roles in growth, digestion, antioxidant defense, immunity, and inflammation regulation in fish. This study investigated the effects of graded dietary Zn levels on growth performance, serum biochemistry, digestive enzyme activity, zinc transporter expression, antioxidant capacity, immune responses, and inflammatory regulation in juvenile black carp (Mylopharyngodon piceus). Six isonitrogenous and isoenergetic diets were formulated to contain 27.95, 34.38, 44.90, 66.52, 116.14, and 199.56 mg/kg Zn by supplementing ZnSO4·7H2O. Juvenile fish with an initial weight of 2.88 ± 0.12 g were fed the experimental diets for 60 days in triplicate tanks. Growth performance increased with dietary Zn and then plateaued at 44.90–199.56 mg/kg; broken-line regression estimated the optimal dietary Zn requirement at 44.6 mg/kg. Adequate Zn supplementation also reduced whole-body lipid content, increased digestive enzyme activities, improved serum HDL-C and ALP levels, and decreased AST and ALT activities. In addition, adequate dietary Zn (44.90 mg/kg) significantly modulated the expression of zinc transporter genes in the liver and intestine. Adequate dietary Zn supplementation enhanced antioxidant capacity by activating the Nrf2/Keap1 signaling pathway, improved intestinal immunity, and strengthened barrier function by increasing the expression of tight junction proteins and mucins. Moreover, adequate dietary Zn could alleviate inflammatory responses by upregulating anti-inflammatory factors and downregulating pro-inflammatory cytokines via the MAPK14 signaling pathway. These findings suggest that dietary zinc at 44.60 mg/kg is sufficient to promote growth, antioxidant status, immune function, and intestinal health in juvenile black carp.