Requirements of vitamin C (L-ascorbyl-2-sulphate and L-ascorbyl-2-polyphosphate) and its effects on non-specific immune responses of grouper, Epinephelus malabaricus.

摘要

An 8-week feeding trial was conducted to determine two vitamin C derivatives, L-ascorbyl-2-sulphate (C2S) and L-ascorbyl-2-polyphosphate (C2PP), to satisfy vitamin C requirement and to test their effects on the non-specific humoral immune responses of juvenile grouper, Epinephelus malabaricus. C2S and C2PP were each supplemented at 20, 50, 80, 150, 250 and 400 mg kg-1 diet in the semi-purified basal diet providing of 7, 16, 28, 55, 86, 142 mg ascorbic acid (AA) equivalent of C2S kg-1 diet and 4, 9, 15, 31, 49, 75 mg AA equivalent of C2PP kg-1 diet, respectively. Basal diet without AA supplemented was included as a control. Each diet was fed to triplicate groups of grouper (mean initial weight: 6.69+or-0.07 g). Fish fed diets with ?28 mg AA equivalent of C2S or ?4 mg AA equivalent of C2PP kg-1 had significantly (P<0.05) greater weight gain (WG) than fish fed the unsupplemented control diet. Liver AA concentrations were higher in fish fed diets with ?16 mg AA equivalent of C2S or ?9 mg AA equivalent of C2PP kg-1 than fish fed the control diet. Alternative pathway of complement activation (ACP) was higher in fish fed diets with ?55 mg AA equivalent of C2S or ?15 mg AA equivalent of C2PP kg-1 than fish fed the control diet. Lysozyme activity was higher in fish fed ?86 mg AA equivalent of C2S or ?15 mg AA equivalent of C2PP kg-1 than fish fed the 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 46.2 mg AA equivalent of C2S kg-1 diet and 17.8 mg AA equivalent of C2PP kg-1 diet, and it also indicated that C2S is approximately 39% as effective as C2PP in meeting the vitamin C requirement for grouper. The data suggest that both C2S and C2PP supplementation support non-specific immune responses of grouper..