Effect of dietary vitamin C on the growth performance, nonspecific immunity and antioxidant ability of red swamp crayfish (Procambarus clarkii)

The dietary vitamin C (VC) requirement of red swamp crayfish (Procambarus clarkii) has not been determined. The aim of this study was to investigate the effects of dietary VC level on growth performance, body composition, nonspecific immunity, and antioxidant capacity of red swamp crayfish and to determine its VC requirement. Six experimental diets (control, VC3, VC6, VC9, VC12 and VC15) with different levels of VC (0.00, 60.13, 126.93, 192.06, 250.12 and 321.38 mg/kg diet, respectively) were fed to juvenile crayfish (average weight: 7.00 +/- 0.01 g) for 70 d. At the end of the growth trial, the highest final body weight, specific growth rate (SGR), and muscle rate all occurred in the VC12 group (P < 0.05). Hepatosomatic index and serum superoxide dismutase activity were the highest in the VC9 group. Compared with the control group, crayfish fed with VC supplemented diets showed significantly higher contents of crude protein and crude lipid in whole-body, and the higher activities of catalase and glutathione peroxidase as well as the glutathione content in the hepatopancreas (P < 0.05). Conversely, the feed conversion ratio and hepatopancreatic malondialdehyde value of crayfish in the VC supplemented groups were significantly reduced relative to that of the control group (P < 0.05). The VC3 to VC15 diets significantly increased the serum activities of phenoloxidase, lysozyme, nitric oxide synthase, acid phosphatase, anti-superoxide anion and nitric oxide concentration, and the total hemocyte count and blood cell respiratory burst activity (P < 0.05). After the crayfish were subjected to the challenge of the white spot syndrome virus, the cumulated mortality rate in the VC supplemented groups was significantly lower than the control (P < 0.05), which was the lowest in the VC12 and VC15 groups. To conclude, VC can be used as a supplement in crayfish feed to increase growth, immunity, and antioxidant capacity. Broken-line regression analysis on SGR indicated that the optimal dietary VC requirement of P. clarkii was estimated to be 265.67 mg/kg diet.