Effects of dietary taurine content on growth performance, body composition, expression of taurine transporter (TauT) mRNA and key enzyme activities of taurine synthesis in juvenile grouper (Epinephelus coioides)

The study was conducted to investigate the effects of different dietary taurine concentrations on growth performance, body composition, tissue mRNA expression of taurine transporter (TauT) and key enzyme activities of taurine synthesis (cysteine sulfinic acid decarboxylase and cysteine dioxygenase, i.e. CSD and CDO) in juvenile grouper (Epinephelus coioides). Four diets at 0 (0DT), 0.5% (0.5DT), 1.0% (1.0DT) and 1.5% (1.5DT) taurine levels were formulated using casein and gelatin as the protein source. A total of 320 juvenile fish with an average weight of (13.85±0.25) g were randomly divided into 4 groups with 4 replicate tanks at a stock density of 20 fish per tank, and each group of fish was fed one of the same experimental diets to apparent satiation each time during a feeding period of 84 days. Results showed that the feed efficiency, feeding rate, weight gain rate and whole-body crude protein content for fish fed the diets with taurine administration were significantly increased, but hepatosomatic index and whole-body crude lipid content were significantly decreased in comparison with 0DT. The dietary taurine addition significantly upregulated tissue mRNA expression levels of TauT and 1.0DT had the highest level of tissue mRNA expression, which declined with concentrations of taurine, but still was significantly higher than 0DT and 0.5DT. There was a positive correlation between concentrations of taurine in serum, liver, intestine and muscle of juvenile E. coioides and dietary taurine content. The CSD activities in liver, muscle and the CDO activities in plasma, liver, intestine and muscle were significantly decreased by dietary taurine administration, however, the plasma CSD activity was not affected by dietary taurine administration. The results suggested that dietary taurine addition could improve the growth performance of juvenile E. coioides, increase whole-body protein deposit, decrease whole-body lipid deposit, enhance the expression level of TauT mRNA and taurine content in tissues, reduce key enzyme actvities of taurine synthesis. The optimal dietary taurine content for juvenile E. coioides was 0.92% based on the regression analysis between weight gain rate and dietary taurine content.