ABSTRACT
The aim of this experiment was used to investigate the effects of different contents of dietary vitamin D3 on the growth performance and antioxidant and innate immune responses in juvenile black carp Mylopharyngodon piceus. Black carp juveniles were fed six levels of dietary vitamin D3 (VD3) (96, 220, 412, 840, 1480, and 3008 IU/Kg) for 9 weeks. Results showed that highest weight gain (WG) and special growth ratio (SGR) were obtained at 534.2 IU/Kg dietary VD3 according to the second-order polynomial regression model. The protein efficiency ratio (PER) of black carp could be significantly increased by 412, 840, and 1480 IU/Kg dietary VD3 (p < 0.05), while the feed conversion ratio (FCR) were reduced by 412, 840, and 1480 IU/Kg dietary VD3 (p < 0.05). Adequate dietary VD3 content (412, 840, and 1480 IU/Kg) could significantly upregulate expression levels of lipoxygenase 5 (LPO 5); increase the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione reductase (GR); and improve GSH contents and total antioxidant capacities (T-AOC) in the liver of black carp. However, glutathione S-transferase (GST) activities and malondialdehyde (MDA) levels were significantly reduced by adequate dietary VD3 content (412, 840, and 1480 IU/Kg) in the fish liver. In addition, 412, 840, and 1480 IU/Kg dietary VD3 could significantly upregulate the mRNA expression levels of interferon-α (IFN-α), lysozyme (LYZ), hepcidin (HEPC), natural resistance-associated macrophage protein (NRAMP), and complement component 3 (C3) and C9 in the hemocytes and liver of black carp juveniles compared with the VD3-deficient diet (96 IU/Kg). Meanwhile, higher contents of dietary VD3 could increase serum LYZ and ACP activities and C3 and C4 contents in black carp juveniles compared with the groups fed VD3-deficient diet. In conclusion, these results suggest that adequate dietary VD3 could increase growth performances, improve antioxidant capacities, and then enhance innate immune parameters in black carp juveniles.