Effects Of Dietary Taurine And Related Amino Acids On Growth Performance And TauT MRNA Expression Of Turbot And Japanese Seabass

This experiment investigated the effects of dietary taurine and related amino acids on growth performance and TauT mRNA relative expression of juvenile turbot and Japanese seabass, and the effects yeast hydrolysate on the non-specific immunity and anti-stress of juvnile turbot. A 10-week or8-week feeding experiment in indoor flowing-through water system was conducted and results of these studies are shown as follows:1. A 10-week feeding experiment in indoor flowing-through water system was conducted to evaluate the effects of taurine, methionine and cysteine in diets on growth performance and taurine transporter(TauT)mRNA expression of juvenile turbot [initial weight:(7.90±0.07) g]. The basal diet was supplemented with 0, 1%, 2% taurine, 0.5% methionine and0.5% cysteine(Control T-0, T-1, T-2, M-0.5 and C-0.5, respectively) to formulate five isonitrogenous and isolipidic diets. The results showed that the specific growth rate(SGR) and feed efficiency(FE) of T-1 and T-2group were significantly higher than that of the control group(P<0.05), and the visceral indexes(VSI) of T-1 and T-2 group was significantly lowerthan that of the control group(P<0.05). Compared with T-0 group, the SGR and FE of M-0.5 group improved(P>0.05), and VSI decreased significantly(P<0.05), while condition factors(CF) increased significantly(P<0.05). Compared with T-0 group, the SGR of C-0.5 group decreased significantly(P<0.05), and no significant differences in FE, VSI and CF were observed(P>0.05) between the two groups. T-1 and T-2 group had significantly lower TauT mRNA relative expression(P<0.05) in liver, brain and eye tissues than those in T-0 group, and the TauT mRNA relative expression in liver, brain and eye tissues decreased significantly(P<0.05)with increasing dietary taurine level. On the contrary, the TauT mRNA relative expression in liver, brain and eye tissues of M-0.5 group was significantly higher(P<0.05) than those in T-0, T-1 and T-2 groups. C-0.5group had a significantly higher TauT mRNA relative expression(P<0.05)in liver, brain and eye than those in T-0, T-1 and T-2 groups, but no significant differences(P>0.05) were found when compared with M-0.5group. In conclusion, 0.48%, 1.06% taurine in diets could promote growth performance of juvenile turbot under these experimental conditions. The TauT mRNA expression in juvenile turbot may be affected by dietary sulfur-containing amino acids such as taurine, methionine and cysteine.2. A 10-week feeding experiment in indoor flowing-through water system was conducted to investigate the effects of dietary taurine,methionine and cysteine on the growth performance, amino acid composition and TauT mRNA expression of Japanese seabass(mean initial weight: 8.13±0.05 g). A basal diet(Control, T-0) with 15% fish meal, 30%soybean meal, 13% corn gluten meal and 12% wheat gluten was formulated. The other four experimental diets were supplemented with 1%,2% taurine, 0.5% methionine and 0.5% cysteine(named T-1, T-2, M-0.5and C-0.5, respectively) to the basal diet to formulate isonitrogenous and isolipidic diets. Triplicate groups of 25 fish were fed to apparent satiation twice daily. During the experimental period, water temperature ranged from23.2-28.8℃, and the dissolved oxygen content was above 7 mg/L. The results showed that the final body weight(FBW),specific growth rate(SGR)and feed intake(FI) of T-1, T-2, M-0.5 and C-0.5 groups were significantly higher than the control group(P<0.05). Fish fed the diets with taurine,methionine and cysteine supplementation had significantly higher whole-body crude protein and crude lipid contents(P<0.05), while the whole-body moisture followed opposite pattern. The taurine contents of liver and muscle in T-1 and T-2 groups were significantly higher than that in T-0 group(P<0.05), however, the taurine contents of liver and muscle in M-0.5 and C-0.5 groups had no different with T-0 group(P>0.05).Compared with the control, fish in T-1, T-2 and C-0.5 groups had higher liver essential amino acids and total amino acids contents(P<0.05), whilethe liver essential amino acids and total amino acids contents in M-0.5group showed no significant difference(P>0.05). The muscle essential amino acids content of T-1, T-2, M-0.5 and C-0.5 groups were higher than T-0 group, but only the M-0.5 group showed siginificant difference with T-0 group(P<0.05). Fish in T-1, T-2 and M-0.5 groups had siginificantly higher muscle total amino acids than T-0 group(P<0.05), whereas fish in C-0.5 group showed no different muscle total amino acids contents with T-0 group(P>0.05). The TauT mRNA expression of liver, muscle, brain and foregut in T-1 and T-2 group were significantly lower than those in T-0group(P<0.05). The liver TauT mRNA expression in M-0.5 and C-0.5group were significantly higher than that in T-0 group(P<0.05), while the brain and foregut TauT mRNA expression in M-0.5 and C-0.5 group were significantly lower than those in T-0 group(P<0.05). The liver and muscle IGF-Ⅰ mRNA expression in T-1, T-2, M-0.5 and C-0.5 group were significantly higher than those in T-0 group(P<0.05). From the above results we can kown that dietary taurine, methionine and cysteine could improve the amino acids deposition in liver and muscle. The TauT mRNA expression in Japanese seabass could be regulated by the dietary sulfur-containing amino acids such as taurine, methionine and cysteine, and these amino acids could improve growth performance through up regulated the IGF-ⅠmRNA expression.3. This study was conducted to investigate the effects of yeast hydrolysate on non-specific immunity, liver antioxidant ability and anti-stress ability of juvenile turbot. The experimental diets employed fishmeal, soybean meal, corn gluten meal, vital wheat gluten and yeast powder as compound protein source, and formulated four kinds of isonitrogenous and isolipidic diets, which contained 0(YH-0), 1%(YH-1),2%(YH-2) and 3%(YH-3) yeast hydrolysate respectively. The feeding trial was conducted in an in-door flowing seawater system for 8 weeks.Triplicate groups of 30 fishes were hand-fed to apparent satiation twice daily. Results show that, the activity of serum lysozyme(LZM), liver acid phosphatase(ACP), nitricoxide synthase(NOS) and liver superoxide dismutase(SOD) in fish fed experimental diets were significantly higher than those in control group(P<0.05). The activity of liver alkaline phosphatase(AKP) in YH-2 and YH-3 was higher than that in control and YH-1(P<0.05). The total antioxidant capacity in the YH-1 group was significantly higher than that in control group(P<0.05). The liver malondialdehyde(MDA) content in group YH-1 and YH-2 was lower than the control group, while the peroxidase(POD) activity was higher than the control group(P>0.05). Furthermore, the time of low salinity tolerance in fish fed test diets was significantly longer than that in control group(P<0.05). In conclusion, the present study suggests that yeast hydrolysatecan improve the non-specific immunity, antioxidant capacity and anti-stress ability for juvenile turbot, and under this experimental condition, it can obtain the best results in YH-2 group.