The Optimal Arginine,lysine And Methionine Requirement In Diets For Juvenile Humpback Grouper,Cromileptes Altivelis

The purpose of this study was to evaluate the effects of dietary arginine,lysine and methionine levels on survival,growth,feed utilization,gut micromorphology,lipid metabolism,oxidation resistance and immunity of juvenile humpback grouper,Cromileptes altivelis,and hence to determine the optimum requirements of these three essential amino acids in diets for this fish species.The main experimental contents and results were as followed:1. The optimal arginine requirement in diets for juvenile humpback grouper,Cromileptes altivelisAn 8-week feeding trial was conducted to evaluate the effects of dietary arginine?Arg?levels on growth performance,gut micromorphology,oxidation resistance and immune responses of humpback grouper,Cromileptes altivelis.Seven isoenergetic?14.23 KJ/g of dry matter?,isoproteic?50%of dry matter?and isolipidic?10%of dry matter?experimental diets were formulated to contain 1.74,2.42,3.14,3.58,4.06,4.54 and 5.21%dietary Arg levels.Triplicate groups of 12 fish?average initial body weight:6.55±0.1g?were fed to apparent satiation by hand twice daily?08:00 h and 16:00 h?in an indoor recirculating seawater system.After the feeding trial,all remaining fish were challenged by 2.5 mg Cu?II?·L^-1,and survival rates were recorded for 12 h.Results showed that weight gain ratio?WGR?,protein efficiency ratio?PER?as well as protein productive value?PPV?of fish were improved with the increments in dietary Arg from 1.74%to 3.58%,and thereafter,values of these parameters displayed a declining trend as dietary Arg level continued to rise from 3.58%to 5.21%.Fish fed 3.14%and3.58%dietary Arg had lower feed conversion ratio?FCR?and daily feed intake?DFI?than fish fed other dietary Arg levels.Hepatosomatic index?HSI?was reduced as dietary Arg level increased.Fish fed 3.58%dietary Arg had higher whole-body content than fish fed other dietary Arg levels.Expression of hepatic insulin-like growth factor-I?IGF-1?,target of rapamycin?TOR?,S6 kinase1?S6K1?and hypothalamus growth hormone receptor?GHR?in fish fed 3.14%and 3.58%dietary Arg was higher than that in fish fed other dietary Arg levels.Gut micromorphology was significantly influenced by dietary Arg levels.After the exposure to 2.5mg Cu?II?·L^-1 water for 12 h,fish fed 3.58%dietary Arg had the highest survival ratios,superoxide dismutase?SOD?,catalase?CAT?activities and immunoglobulin M?Ig M?concentrations in serum among all experimental groups.Fish fed3.14%dietary Arg had the highest expression of NF-E2-related factor 2?Nrf2?and heat shock proteins genes 70?HSP70?in head kiney.Quadratic regression analysis of WGR against dietary Arg levels indicated that optimal dietary Arg level for maximum growth of humpback grouper was 3.39%of dry matter?6.78%of dietary protein?.2. The optimal lysine requirement in diets for juvenile humpback grouper,Cromileptes altivelisA ten-week growth trial was conducted to evaluate the optimum lysine?Lys?requirement in diets for juvenile humpback grouper,Cromileptes altivelis.Seven isoenergetic?14.23 KJ/g of dry matter?,isoproteic?50%of dry matter?and isolipidic?10%of dry matter?experimental diets were formulated to contain graded Lys levels,ranging from 1.91%to 4.76%of dry matter.Experimental fish?initial average body weight:6.8±0.1 g?were randomly distributed into 21 glass tanks?length 60 cm×width 45 cm×height50 cm?at a density of 11 fish/tank.Results showed that growth and feed utilization of fish were significantly affected by different dietary Lys levels.Fish fed 1.91%dietary Lys had significantly lower survival than fish fed other dietary Lys levels.Fish fed 3.84%dietary Lys had the highest WGR among all experimental groups,and fish fed 3.38%or 3.84%dietary Lys showed the highest PER and the lowest FCR.Fish fed the diet with 3.38%Lys showed highest PPV compared with those fed the other diets.The quadratic regression analysis of WGR,PER,PPV and FCR against dietary Lys levels indicated that the optimum dietary Lys requirement for humpback grouper was estimated to be 3.99,3.54,3.42 and 3.62%of dry matter,respectively.Gut micromorphology including villous height?h F?,villous width?w F?and microvillus height?h MV?in foregut and midgut were elevated by suitable Lys supplementations to diets.Fish fed 3.84%dietary Lys had higher expression of growth hormone?GH?,GHR in hypothalamus,and IGF-1,TOR,S6K1 in liver than fish fed other dietary Lys levels.In conclusion,the optimum dietary Lys requirement for maximal WGR of humpback grouper was estimated to be 3.99%of dry matter?corresponding to 7.98%of dietary protein?.3. The optimal methionine requirement in diets for juvenile humpback grouper,Cromileptes altivelisAn 8-week feeding trial was conducted to evaluate the effects of dietary methionine?Met?levels on growth performance,feed utilization,gut micromorphology and lipid metabolism of humpback grouper,Cromileptes altivelis.Seven isoenergetic?14.23 KJ/g of dry matter?,isoproteic?48.91%of dry matter?and isolipidic?10%of dry matter?experimental diets were formulated to contain 0.70?0.88?1.04?1.27?1.46?1.61and 1.76%dietary Met levels.Triplicate groups of 14 fish?average initial body weight:6.57±0.14g?were fed to apparent satiation by hand twice daily?08:00 h and 16:00 h?.Results showed that growth,feed utilization,gut micromorphology and lipid metabolism of juvenile humpback grouper were significantly affected by different dietary Met levels.Fish fed 0.70%and 0.88%dietary Met had lower survival ratio and WGR than fish fed other dietary Met levels.The trend of variations for PER and PPV was similar to WGR,while DFI and FCR had an opposite one to WGR.Fish fed 0.70%dietary Met had the highest HSI,the lowest intestinal somatic index?ISI?and condition factor?CF?among all experimental treatments.Fish fed 0.70%and 0.88%dietary Met had the lower protein and lipid content in whole body and white muscle than fish fed other dietary Met levels.Gut micromorphology including h V,w V,h E,h MV in fish fed 0.70%dietary Met were lower than those in fish fed other dietary Met levels.Fish fed 0.70%dietary Met had highest expression of hepatic general control nonderepressible2?GCN2?,CCAAT enhancer binding protein??C/EBP??,peroxisome proliferator activated receptor??PPAR??and carnitine acyl transferase-1?CPT-1?but lowest expression of brain GH,GHR,hepatic IGF-1,TOR,S6K1,fatty acid synthetase?FAS?and sterol regulatory element binding protein-1?SREBP-1?among all the experimental treatments.Based on the analysis of the straight broken-line regression of WGR,FCR,PER or PPV against dietary Met levels,the optimum dietary Met requirement for humpback grouper was estimated to be 1.05-1.11%of dry matter?corresponding to 2.15-2.27%of dietary protein on a dry weight basis?.