Effect Of Dietary Taurine Level On The Growth Performance And The Activities Of Key Taurine Biosynthesis Enzymes In Tilapia Oreochromis Nilotictus And Grouper Epinephelus Coioides At Different Feed Periods

Two experiments were conducted to investigate the effect of dietary taurine level on the growth performance, body composition, tissue free amino acid concentrations and the activities of key taurine synthesis enzymes in grouper(Epinephelus coioides) and tilapia(Oreochromis nilotictus). The results are presented as follows:1. Effect of dietary taurine level on the growth performance and body composition in tilapia and grouperTilapias(about 4.25 g of initial body weight) were randomly divided into four groups with four replicate tanks(Volume of 120 L) at a stock density of twenty five fish in each replicate, as was the anrangement for grouper(about 13.85 g of initial body weight). Four tilapia diets were formulated to contain taurine at 0%(DT1), 0.4%(DT2), 0.8%(DT3), and 1.2%(DT4) and four grouper diets were formulated to contain taurine at 0%(DG1),0.5%(DG2),1.0%(DG3), and 1.5%(DG4). Groups of fish were fed one of the diets twice daily across an 84-day period for each feeding trial. Tilapia: at day 28, weight gain rate increased from DT1 to DT3, then DT4 decreased, and weight gain rate was highest at DT3 and was higher than those of other taurine treatments; at day 56 and day 84, there were similar trend with these growth parameters with the increase in dietary taurine level; The hepatosomatic index and viscerasomatic index in taurine-treated groups were significantly higher than that of the control, however, no differences in feed efficiency, condition factor and survival were found among dietary treatments at each feed period; The whole-body moisture contents were lower, but whole-body curde ptotein and the crude lipid contents were higher in taurine-treated groups than that in control; Dietary taurine treatment did not affect whole-body ash content. Grouper: the similar trend of fish growth was observed either at day 28, 56 or 84 in response to dietary taurine level, and this trend followed the the change observed in tilapia growth trial; The hepatosomatic index and viscerasomatic index in taurine-treated groups were significantly higher than that of the control, but condition factor and survival were not affected by dietary taurine level; The whole-body curde protein contents were higher, but curde lipid contents lower than that in control; these were no differences in moisture and ash contents among treatments. The results indicate that fish growth is affected markedly by dietary taurine level, and the requirement for taurine declines along with fish growth of age.2. Effects of dietary taurine on free amino acid and taurine concentrations in tissues of tilapia and grouperAfter the end of the feeding trial, plasma, liver, muscle and intestinal tract were sampled to determine the free amino acid and taurine concentrations. Free amino acid contents in plsama of both tilapia and grouper gradually decreased with the increase in dietary taurine, and free amino acid concentrations in taurine-treated groups were significantly lower than that in control group. Free amino acid concentrations of all groups increased along with the growth of age in both tilapia and grouper; increasing dietary taurine level, promoted taurine concentrations in liver, muscle and intestinal tract. Taurine concentrations in taurine-treated groups were significantly higher than that in control group. Taurine concentrations in liver, muscle and intestinal tract increased with the growth of age in both tilapia and grouper.3. Effects of dietary taurine on CSAD and CDO activities in tissues of tilapia and grouperAt the termination of the feeding trial, the liver, muscle, plasma and intestinal tract were sampled to determine the key enzyme activity of taurine synthesis in tilapia and grouper. Increasing dietary taurine level led to increased CSAD and CDO activities in plasma, liver, muscle and intestinal tract of tilapia and grouper, and CSAD and CDO activities in taurine-treated groups were significantly lower than that in control group. CSAD and CDO activities of all groups increased with the growth age of tilapia and grouper.