Effects of dietary vitamin C on growth, antioxidant activity, and immunity in ricefield eel ( Monopterus albus )

A 10‐week feeding trial aimed to investigate the effects of dietary vitamin C ( l ‐ascorbic acid) on growth, antioxidant activity, and immunity in ricefield eel, Monopterus albus . Six diets were formulated with different levels of vitamin C supplementation (0.1, 17.5, 34.8, 68.6, 139.7, and 278.5 mg/kg). The results indicated that the weight gain (WG) of the M. albus fed the diets with vitamin C was remarkably higher than that of the M. albus fed the control diet ( p  < .05), and the quadratic analysis showed an optimal vitamin C level of 80.66 mg/kg. Compared with the control group, serum lysozyme activities, the complement pathway, red blood cell counts, white blood cell counts, immunoglobulin M, and phagocytosis percentage were significantly increased ( p  < .05) in the treatment groups, and superoxide dismutase activity, serum glucose, and malondialdehyde content were significantly decreased ( p  < .05) in the treatment groups. The challenge trial with Aeromonas hydrophila showed that the M. albus fed the diets with vitamin C had remarkably reduced cumulative mortality compared with those fed the control diet ( p  < .05), and mortality in the 68.60 mg/kg diet group was the lowest. Based on WG, the optimal vitamin C supplementation level for M. albus was estimated to be 80.66 mg/kg.