Taurine requirement and metabolism response of tiger puffer Takifugu rubripes to graded taurine supplementation

Abstract

An eight week feeding trial was conducted to investigate the effect of taurine supplementation on growth performance, sulfur amino acid concentrations, the activity and gene expression of enzymes related to taurine synthesis, and gene expression of taurine transporter (TAUT) in tiger puffer (Takifugu rubripes). Test diets were respectively supplemented with 0, 3, 6, 9, 12 and 20 g kg−1 taurine (the T0, T3, T6, T9, T12 and T20 diets) and a control diet was supplemented with 12 g kg−1 cysteine (the Cys diet). All experimental diets were fed to triplicate groups of 25 fish (initial weight 20.05 ± 0.06 g). Dose responses were observed in terms of specific growth rate and feed efficiency ratio. Dietary taurine requirement was estimated at 5.25 and 8.23 g kg−1 of dry matter of the diet based on regression analysis for specific growth rate and feed efficiency ratio, respectively. Free taurine concentrations of muscle and liver tissues increased with the increase of dietary taurine concentration. However, there was no significant difference in free taurine concentrations in muscle or liver between the Cys and T0 groups (p > .05). Free methionine concentration of liver tissue gradually increased with the increase of dietary taurine, which implied that exogenous taurine appeared to spare hepatic methionine. Cysteine sulfinic acid decarboxylase (CSD) activity and mRNA level in liver were down-regulated in the T9, T12 and T20 groups compared with the T0 group (p < .05), while no statistical difference was observed in cysteine dioxygenase (CDO) activity and expression between the T0 group and the taurine supplementation groups (the T3, T6, T9, T12 and T20 groups (p > .05). TAUT mRNA levels in muscle had a decrease trend in fish fed diets containing 1.7 to 8.2 g kg−1 taurine (the T0, T3 and T6 groups), while there was no significant difference when dietary taurine concentrations increased from 8.2 to 21.9 g kg−1 (the T6, T9, T12 and T20 groups). In conclusion, tiger puffer cannot synthesize taurine in the liver at the level of cysteine used in this study, whereas a sparing effect on the methionine demand may be observed in liver by dietary taurine supplementation. Our data indicates that taurine is a conditionally essential amino acid for tiger puffer, and the taurine requirement was estimated ranged from 5.25 to 8.23 g kg−1 of dry matter of the diet.