The effects of dietary vitamin C on growth performance, serum enzymes activities and resistance to Vibrio alginolyticus challenge of yellow drum Nibea albiflora

A 9-week feeding trial was conducted to determine the optimal dietary vitamin C requirement and its effects on serum enzymes activities and bacterial resistance in the juvenile yellow drum Nibea albiflora (initial weight 33.2 +/- 0.10g). Six practical diets were formulated containing vitamin C 2.1, 45.3, 89.6, 132.4, 178.6 and 547.1mgkg(-1) diet supplied as l-ascorbyl-2-monophosphate. The fish fed 547.1mgkg(-1) diet showed a significantly higher survival than that fed 2.1mgkg(-1) diet. The weight gains and specific growth rate of the fish fed 2.1mgkg(-1) diet were significantly lower than those of the fish fed 89.6-547.1mgkg(-1) diets. The liver vitamin C concentration firstly increased with increasing dietary vitamin C supply from 2.1 to 178.6mgkg(-1) diet and then stabilized. The serum superoxide dismutase activities of the fish fed 547.1mgkg(-1) diet were significantly lower than those of the fish fed 2.1-89.6mgkg(-1) diet. The fish fed 2.1mgkg(-1) diet had a significantly higher alkaline phosphatase activity than those in the other groups except the 45.3mgkg(-1) group. Fish that received diets containing vitamin C at 547.1mg kg(-1) had significantly higher nitro blue tetrazolium and lysozyme activity, and fish that received diets containing vitamin C at 45.3-547.1mg kg(-1) exhibited resistance against Vibrio alginolyticus infection. The dietary vitamin C requirement of the juvenile yellow drum was established based on broken-line model of weight gain to be 142.2mg l-ascorbyl-2-monophosphate kg(-1) diet.