Ascorbic acid enhanced the growth performance, oxidative status, and resistance to Aeromonas hydrophila challenge of juvenile grass carp ( Ctenopharyngodon idella )

This study was conducted to examine the dietary ascorbic acid requirement and effects on growth performance, oxidative status, and disease resistance in juvenile grass carp ( Ctenopharyngodon idella ). Triplicate groups of 30 fish weighting 3.39 ± 0.03 g were fed with diets containing graded levels of ascorbic acid (18.9, 71.8, 118.7, 169.9, 321.1, and 618.5 mg kg −1 ) in a recirculating rearing system for 8 weeks. No significant differences in growth performance among all groups were observed ( P > 0.05). Diet with 321.1 mg kg −1 ascorbic acid significantly increased the feed intake ( P < 0.05). Meanwhile, the expression of liver peroxisome proliferator-activated receptors-γ and uncoupling protein 2 were significantly declined ( P < 0.05). Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila (2.4 × 10 5 CFU cells mL −1 per fish) and fish fed with ascorbic acid shown a better liver oxidation status (e.g., superoxide dismutase and glutathione peroxidase) than the control diet ( P < 0.05). The optimum dietary ascorbic acid concentration was about 155 mg kg −1 basing on the oxidation status in liver. Nevertheless, the broken-line model indicated that the optimal level for juvenile grass carp is about 310 mg kg −1 .