Requirements of vitamin C (L-ascorbyl-2-monophosphate-Mg and L-ascorbyl-2-monophosphate-Na) and its effects on immune responses of grouper,Epinephelus malabaricus.

An 8-week feeding trial was conducted to evaluate two vitamin C derivatives, L-ascorbyl-2-monophosphate-Mg (C2MP-Mg) and L-ascorbyl-2-monophosphate-Na (C2MP-Na), to satisfy the vitamin C requirement and to test their effects on the immune responses of juvenile grouper,Epinephelus malabaricus. C2MP-Mg and C2MP-Na were each supplemented at 20, 50, 80, 150, 250, and 400 mg kg−1 diet in the basal diet providing of 7, 18, 31, 51, 93, 145 mg ascorbic acid (AA) equivalent of C2MP-Mg kg−1 diet and 4, 10, 17, 31, 47, 77 mg ascorbic acid (AA) equivalent of C2MP-Na kg−1 diet, respectively. Basal diet without AA supplementation was included as control. Each diet was fed to triplicate groups of grouper (mean initial weight 3.20 ± 0.05 g). Fish fed diets supplemented with either C2MP-Mg or C2MP-Na had significantly (P < 0.05) greater weight gain (WG), feed efficiency and survival than those fed the unsupplemented control diet. Liver ascorbate concentrations in fish generally increased as dietary C2MP-Mg or C2MP-Na supplementation level increased. Haemolytic complement activity was higher in fish fed diets supplemented with 92 mg AA equivalent of C2MP-Mg kg−1 or 10–17 mg AA equivalent of C2MP-Na kg−1 than fish fed the unsupplemented control diet. Lysozyme activity was higher in fish fed≥51 mg AA equivalent of C2MP-Mg kg−1 or≥47 mg AA equivalent of C2MP-Na kg−1 than fish fed the unsupplemented control diet. Analysis by broken-line regression of WG indicated that the adequate dietary vitamin C concentration from each vitamin C derivative in growing grouper is 17.9 mg AA equivalent of 2MP-Mg kg−1 and 8.3 mg AA equivalent of C2MP-Na kg−1, and it also indicated that C2MP-Mg is about 46% as effective as C2MP-Na in meeting the vitamin C requirement of grouper. [ABSTRACT FROM AUTHOR]