Research On The Application Of Three Plant-Derived Proteins In Low Fish Meal Diets Of Juvenile Hybrid Grouper (Epinephelus Fuscoguttatus ♀ × Epinephelus Lanceolatus ♂)

The main aim of this thesis was to study the possible replacing potential of alternative nonFM protein sources(soybean protein isolate,common cottonseed protein and low-gossypol cottonseed protein)to poultry by-product meal protein(PBMP)in low-FM diets of hybrid grouper.The main experimental contents and results were as followed:1.The replacing potential of soybean protein isolate to poultry by-product meal protein in low-FM diets of juvenile hybrid grouper.The replacing potential of soybean protein isolate to poultry by-product meal protein in low-FM diets of juvenile hybrid grouper was studied through a seven-week growth trial and meanwhile,the effect of individual arginine(Arg)and methionine(Met)supplementation on sparing dietary crude protein was also studied.Eight experimental diets were formulated,including six isoproteic(49% of dry matter),isolipidic(9%)and isoenergetic(340 kcal per 100 g dry matter)low FM diets and two high FM diets.In low FM diets,0(SPIP0),20%(SPIP20),40%(SPIP40),60%(SPIP60),80%(SPIP80)and 100%(SPIP100)of PBM protein were replaced by SPI protein,respectively.The two high FM diets were designed as followed: one had high protein(53.5%)(HFMHP)with no individual arginine and methionine,and the other had relatively low protein(49%)(HFMLP)as well as supplemented with arginine and methionine.Randomly divide the fish into 12 fish per fish tank(average initial body weight:13.30±0.1 g),triplicate groups for each diets group,and ensure that they are fed twice daily(08:00h and 16:00h).Experimental data indicated that weight gain percentage(WG%),protein efficiency ratio(PER)as well as protein productive value(PPV)of fish fed HFMHP were significantly lower than that of fish fed FMLP,SPIP20,SPIP40 and SPIP60(P<0.01).Among fish fed low-FM diets,WG%,PER as well as PPV were elevated with the increment in PBMP replacements,reaching the peak value at the 60% replacing level,and then they were reduced at the 80% or100% replacing level.Analysis of the straight broken-line model showed that the maximum PBMP replacement level by SPIP at the intercept value of WG% was estimated to be 60%.Feed conversion ratio(FCR)showed an opposite tendency of variation to WG%.Fish fed SPIP80 and SPIP100 displayed lower m RNA levels of insulin like growth factor-1(IGF-1)in liver,neuropeptide Y(NPY)in hypothalamus as well as NF-E2-related factor 2(Nrf2)in head kidney than fish fed other experimental diets.Generally,60%of PBM protein could be replaced with SPI protein in hybrid grouper fed low FM diets,and supplementation of individual Arg and Met to their optimum requirements had an effect on sparing dietary protein.2.Effects of replacing poultry by-product meal protein with common cottonseed protein or low-gossypol cottonseed protein in low-FM diets of juvenile hybrid grouper.A nine-week growth trial was conducted to evaluate the replacing potential of soybean protein isolate(SPI)to poultry by-product meal(PBM)protein in low-FM diets of juvenile hybrid grouper.Twelve isoenergetic(340 kcal per 100 g of dry matter),isoproteic(46.46% of dry matter)and isolipidic(8.5% of dry matter)experimental diets.The fish meal group(FMP1)was used as the control group.In the low fish meal diets,0(HGCMP0),20%(HGCMP20),40%(HGCMP40),60%(HGCMP60),and then 0(LGCMP0),20%(LGCMP20),40%(LGCMP40),60%(LGCMP60),80%(LGCMP80)and 100%(LGCMP100)of PBM protein were replaced by low-gossypol cottonseed protein,respectively.Experimental cages were labeled and located in twelve connective 12-m3 indoor concrete tanks(L3m × W4 m × H1m)with 6 cages(L1.3m ×W0.8m × H0.8m)in each tank.Randomly divide the fish into 14 fish per tank(average initial body weight: 14.30 ± 0.1 g),triplicate groups for each diets group,and ensure that they are fed twice daily(08:00h and 16:00h).Experimental data indicated that feed utilization,growth performance,body composition and immunohematological for fed all experiment diets were significantly lower compared to fish fed the reference diet.The weight gain percentage of experimental fish was firstly increased and then decreased with the replacement level of common cottonseed protein or low-gossypol cottonseed protein.The weight gain rate(WG %)of(FMP1),HGCMP80 and LGCMP40 was significantly higher than that other feed groups of fish(P<0.01).The moisture content of body or muscle of juvenile hybrid grouper increased gradually with the replacement levels of poultry by-product meal protein by common cottonseed protein or low-gossypol cottonseed protein in the diet,and the body fat content showed an opposite tendency of variation to moisture content of fish.The HV and WV of foregut and hindgut of experimental fish were firstly increased and then decreased with the replacement levels of common cottonseed protein or low-gossypol cottonseed protein.HV and WV reached the maximum value when common cottonseed protein replaced 80%(HGCMP80)of poultry by-product meal protein,or at the 40% replacing level(LGCMP40)by low-gossypol cottonseed protein.Fish fed HGCMP and LGCMP100 displayed lower m RNA levels of insulin like growth factor-1(IGF-1)in liver and AGRP in hypothalamus than fish fed other experimental diets.In addition,the concentrations of serum LZM and Ig M of fish fed PBMP were lower than those of other experimental groups.Generally,analysis of the cubic curve model showed that the maximum PBMP replacement level by common cottonseed protein at the intercept value of WG% was estimated to be 74%,and analysis of the secondorder polynomial model showed that the maximum PBMP replacement level by low-gossypol cottonseed at the intercept value of WG% was estimated to be 33%.