Effects Of Dietary Small Molecular Nitrogen Compounds And Krill Hydrolysates On Growth Performance And Expression Of Growth Related Genes Of Juvenile Turbot(Scophthalmus Maximus L.)

The current study investigated the effects of dietary small molecular nitrogen compounds and krill hydrolysates on growth performance and expression of growth related genes of juvenile turbot(Scophthalmus maximus L.)with a 10-week feeding trial using indoor flowing-through water system.The results of these studies are shown as follows:1.The study investigated the effects of dietary small molecular nitrogen compounds on growth performance,body composition,intestinal morphology,related enzyme activities and growth related genes of juvenile turbot [(initial weight of(9.46±0.01)g] fed with high plant protein.There were Six isonitrogenous and isolipidic diets were formulated for 10-week feeding experiment in indoor flowing-through seawater system.A 30% fish meal positive(FM),a negative control(SB)with soybean meal in exchange of 30% fish meal protein and four more SB diets were produced added 1% taurine(SBT),0.6% hydroxyproline(SBH),0.03% nucleotide mix(SBN),0.39% carnosine(SBC).Fish fed SB diet obtained the significantly lower specific growth rate(SGR),protein efficiency ratio(PER)and protein productive value(PPV)than the control group(P<0.05),and there was no significant difference with those in SBN group and SBC group(P>0.05).Compared with fish fed SB group,there exist significantly increase of SGR in fish fed SBT diet and feeding rate(FI)in fish fed SBT,SBH,SBN and SBC diet(P<0.05)as well as PER and PPV in fish fed SBT and SBH diet(P<0.05),and no significant difference was observed with those in the control group(P>0.05).Fish fed diet SBT,SBH,SBN,SBC had significantly higher total amino acid and total essential amino acid than those in SB group and control group(P<0.05).In comparation with fish fed SB diet,both of SBT group and SBN group indicated significantly lower glutamic oxalacetic transaminase(GOT)activities(P<0.05)and SBH group showed the lowest glutamic-pyruvic transaminase(GPT)activities in serum(P<0.05),while those in liver showed the opposite trend.Amylase activity in intestines of fish fed SBH diet and trypsin activities in pyloric caecum of fish fed SBT and SBH diet showed significantly higher than those of fish fed SB diet(P<0.05).Meanwhile,the intestinal morphology analysis showed all of the mid-intestine fold height in SBT and SBC group,enterocyte height in SBH and SBC group,and microvillus height in SBT,SBH and SBN group increased significantly than those in fish fed diet SB(P<0.05).The results also showed that in addition to slightly higher IGF-1 m RNA relative expression of fish fed diet SBN(P<0.05),dietary diets supplementation with small molecular nitrogen compounds had significantly higher IGF-1,NPY,Pep T1 m RNA relative expression than those in fish fed diet SB(P<0.05).In conclusion,these results indicated that dietary small molecular nitrogen compounds supplementation with soybean in exchange of 30% fish meal significantly enhanced the feeding intake and intestinal morphology as well as up-regulated IGF-1,NPY,Pep T1 m RNA relative expression of juvenile turbot.Furthermore,dietary 1% taurine supplementation with soybean in exchange of 30% fish meal protein obtained the best growth performance of juvenile turbot.2.A 10-week feeding experiment in indoor flowing-through seawater system was conducted to investigate the effects of dietary krill hydrolysates on growth performance,body composition,intestinal morphology,related enzyme activities and growth related genes of juvenile turbot [(initial weight of(9.46±0.01)g].Three isonitrogenous and isolipidic diets were formulated to contain 0(Control),5%(LKH),10%(HKH)krill hydrolysates for substitution of fish meal protein in basal diet that includes 30% fish meal,respectively.The results showed that the SGR,FE,PER and PPV in HKH group were significantly higher than those in the control group(P<0.05),but the FI was lower than that of the control group significantly(P<0.05).HKH supplementatation had significantly higher whole-body moisture,whole-body crude protein contents and whole-body lipid contents than those in the control group(P<0.05).Both LKH and HKH groups significantly enhanced the muscle total amino acids contents and essential amino acids content compared with control group(P<0.05).Compared with the control group,both LKH and HKH significantly induced GOT activities in liver(P<0.05)but not GOT activities in serum.HKH group showed the highest GPT activities in liver and the lowest GPT activities in serum(P<0.05).HKH group significantly increased amylase activity in intestines(P<0.05).The increasing amount of krill hydrolysates supplied in diet first decreased and then increased trypsin activities in pyloric caecum and intestines,and HKH group had significantly higher trypsin activities in pyloric caecum and intestines than those in the control group(P<0.05).The fold height of mid-intestine in LKH group and HKH group were significantly higher than that in the control group(P<0.05).Compared to the control group,both of IGF-1 gene in liver and Pep T1 gene in pyloric caecum and proximal intestine had significantly higher m RNA expression in HKH group(P<0.05),while the m RNA expression of NPY gene in brain was significantly higher in HKH group and LKH group(P<0.05).In conclusion,10% krill hydrolysates supplementation in diets could enhance growth performance,up-regulate the m RNA expression of IGF-1,Pep T1,NPY genes,increase the digestive enzyme activity and mid-intestine fold height and promote nutrient digestion and absorption as well as amino acid deposition of juvenile turbot.