The effects of dietary vitamin C on growth performance, serum enzymes activities and resistance toVibrio alginolyticuschallenge of yellow drumNibea albiflora

Abstract

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 ± 0.10 g). Six practical diets were formulated containing vitamin C 2.1, 45.3, 89.6, 132.4, 178.6 and 547.1 mg kg−1 diet supplied as l-ascorbyl-2-monophosphate. The fish fed 547.1 mg kg−1 diet showed a significantly higher survival than that fed 2.1 mg kg−1 diet. The weight gains and specific growth rate of the fish fed 2.1 mg kg−1 diet were significantly lower than those of the fish fed 89.6–547.1 mg kg−1 diets. The liver vitamin C concentration firstly increased with increasing dietary vitamin C supply from 2.1 to 178.6 mg kg−1 diet and then stabilized. The serum superoxide dismutase activities of the fish fed 547.1 mg kg−1 diet were significantly lower than those of the fish fed 2.1–89.6 mg kg−1 diet. The fish fed 2.1 mg kg−1 diet had a significantly higher alkaline phosphatase activity than those in the other groups except the 45.3 mg kg−1 group. Fish that received diets containing vitamin C at 547.1 mg kg−1 had significantly higher nitro blue tetrazolium and lysozyme activity, and fish that received diets containing vitamin C at 45.3–547.1 mg 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 142.2 mg l-ascorbyl-2-monophosphate kg−1 diet.