Effect of dietary ascorbic acid on growth and non-specific immune responses of tiger puffer, Takifugu rubripes

We report nutritional physiology and non-specific immune responses of ascorbic acid (AA) in puffer fish for the first time. This study aimed to examine the essentiality and requirements of AA in diets for the tiger puffer, Takifugu rubripes based on growth performance, liver AA and bone collagen concentration, and non-specific immune responses. Five casein-gelatin based semi-purified diets were formulated to contain five graded levels Of L-ascorbyl-2-monophosphate at 0, 40, 80,160 and 700 mg/kg (designated as AMPO, AMP40, AMP80, AMP160 and AMP700, respectively) and fed to triplicate groups of fish. After 10 weeks of feeding trial, growth performances of fish (initial body weight, 35 g) fed the AMPO were significantly lower compared to that of fish fed diets supplemented with AMP. The fish fed the AMPO diet also exhibited significantly lower hematocrit, condition factor and hepatosomatic index compared to the fish fed diets supplemented with AMP Phagocytic activity (NBT assay) was significantly lower in fish fed the AMPO diet than in fish fed the AMP containing diets. Plasma lysozyme activity of fish fed the AMP80 and AMP160 was significantly higher than that of fish fed the AMPO. Dietary supplementation of AMP significantly increased the liver superoxide dismutase in the fish. Myeloperoxidase activity of fish fed the AMPO was significantly lower compared to that of fish fed the AMP containing diets. Bone collagen level tended to increase numerically and total AA concentration in liver of fish was significantly increased in a dose dependent manner by the supplementation of AMP Therefore, tiger puffer requires exogenous ascorbic acid and the optimum dietary level could be 29 mg AA/kg diet for normal growth and physiology. Dietary AA concentration over 82 mg/kg could be required to enhance non-specific immune responses of the fish. However, it does not seem that the fish needs an overdose of dietary AA (>160 mg/kg) for better non-specific immune responses. (C) 2008 Elsevier Ltd. All rights reserved.