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-gamma and uncoupling protein 2 were significantly declined (P < 0.05). Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila (2.4 x 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).