Dietary vitamin C and its derivatives affect immune responses in grass shrimp, Penaeus monodon

Effects of L-ascorbic acid (AA) and its four derivatives, namely L-ascorbyl-2-sulfate (C2S), L-ascorbyl-2-polyphosphate (C2PP), L-ascorbyl-2-monophosphate-Na (C2MP-Na) and L-ascorbyl-2-monophosphate-Mg (C2MP-Mg) on the immune responses of juvenile grass shrimp, Penaeus monodon, were studied. The vitamin C deprived diet together with diets supplemented with either adequate or high (five times adequate) levels of AA, C2S, C2PP, C2MP-Na and C2MP-Mg were each fed to triplicate groups of shrimp (mean initial weight: 0·37±0·01 g) for 8 weeks. Significantly (P< 0·01) higher weight gain (WG), feed efficiency (FE), survival, total haemocyte count (THC), superoxide anion (O−2) production ratio and phenoloxidase (PO) activity were observed in shrimp fed diets supplemented with adequate and high levels of ascorbate than shrimp fed the vitamin C deprived diet, regardless of the ascorbate source. Among the ascorbate sources, shrimp fed C2MP-Mg and C2PP containing diets had higher THC than shrimp fed AA, C2S and C2MP-Na containing diets, regardless of the supplementation level. Shrimp fed adequate levels of C2MP-Mg and C2PP and high levels of C2MP-Mg containing diets had higher O−2 production ratios than shrimp fed AA and C2S containing diets. Shrimp fed adequate levels of C2MP-Mg and C2PP and high levels of C2PP containing diets had higher PO activity than shrimp fed AA, C2S and C2MP-Na containing diets. These data suggest that dietary ascorbate enhances immune responses in P. monodon and different ascorbate sources may affect the immune responses differently.