The Study Of Complete Fish Meal Replacement By Rice Protein Concentrate In Practical Diets Of Blunt Snout Bream(Megalobrama Amblycephala)

This study was conducted to investigate the effects of complete fish meal replacement by rice protein concentrate with the supplementations of lysine,taurine,protease and cottonseed meal protein hydrolysate on Megalobrama amblycephala.Several key parameters were evaluated including growth performance,flesh quality,muscle development,intestinal digestive and absorptive capability,amino acid metabolism,intestinal morphology,intestinal and hepatic cell proliferation,and the expressions of growth-related genes.This study aimed to evaluate the effectiveness of complete fish meal replacement by rice protein concentrate and several feed additives in aquafeed and provide theoretical basis for the development of fishmeal-free diets of Megalobrama amblycephala.The study included two parts:Experiment 1 Effects of complete fish meal replacement by rice protein concentrate with lysine supplement on growth performance,intestinal digestive and absorptive capability and amino acid metabolism of blunt snout bream(Megalobrama amblycephala)This study was conducted to evaluate the effects of complete fish meal(FM)replacement by rice protein concentrate(RPC)with supplementation of microcapsule lysine(ML)or crystalline lysine(CL)on growth performance,flesh quality,muscle development,intestinal digestive and absorptive capacity and amino acid metabolism of blunt snout bream.Four isonitrogenous and isoenergetic diets were formulated,including FM diet(containing 50 g kg-1 FM),RPC diet(FM replaced by RPC),MRPC diet(FM replaced by RPC with 0.43%ML supplementation)and CRPC diet(FM replaced by RPC with 0.23%CL supplementation).Fish fed FM diet had significantly higher weight gain,feed efficiency,protein efficiency ratio and nitrogen and energy utilization than that of RPC group(P<0.05),but showed no statistical difference with other treatments(P>0.05).Furthermore,no significant difference was found in whole-body proximate compositions,muscle colour,texture and sensory quality(P>0.05).In addition,fish fed RPC diet showed higher muscle fiber frequency in the 20-50 μm class and lower>50 μm class than that of the other groups(P<0.05),but no significant difference was found in frequency distribution of<20 μm diameter fibers(P>0.05).Fish fed RPC diet showed lower activities of intestinal protease,lipase,Na+,K+-ATPase,alkaline phosphatase,creatine kinase and γ-glutamyl transpeptidase than that of the FM group(P<0.05).No significant difference was found in these parameters among fish fed MRPC,CRPC and FM diets(P>0.05).Fish fed RPC diet showed lower hepatic activities of aspartate aminotransferase and alanine aminotransferase but higher activity of succinode hydrogenase than that of the other groups(P<0.05).Fish fed RPC diet showed lower plasma contents of Met,Phe,Lys,His,total protein and albumin but higher urinary nitrogen than that of the other groups(P<0.05).In addition,Fish fed FM diet showed higher plasma Tau content than that of the other groups(P<0.05).No significant difference was observed in activities of intestinal amylase,hepatic xanthine oxidase and plasmatic aspartate aminotransferase and alanine aminotransferase among all groups(P>0.05).Complete FM replaced by RPC had several effects on growth performance,muscle development,intestinal digestive and absorptive capacity and amino acid metabolism for blunt snout bream.However,the negative effects could be recovered with supplementation of ML or CL in practical diet.Experiment 2 Effects of complete fish meal replacement by rice protein concentrate and its optimization on growth performance,intestinal morphology and the expressions of growth-related genes of blunt snout bream(Megalobrama amblycephala)An 8-week feeding experiment was conducted to evaluate the effects of complete fish meal(FM)replacement by rice protein concentrate(RPC)with the supplementation of microcapsule lysine(ML),taurine,protease and cottonseed meal protein hydrolysate(CMH)for blunt snout bream.Several key parameters were evaluated including growth performance,intestinal morphology,hepatic and intestinal cell proliferation,and the expressions of genes involved in the growth hormone(GH)-insulin-like growth factor-I(IGF-I)axis,target of rapamycin(TOR)signaling pathway,myogenic regulatory factors(MRFs)and myostatin(MSTN).A total of six isonitrogenous and isoenergetic diets were formulated,including FM diet(containing 5%FM),RPC diet(FM replaced by RPC),MRPC diet(RPC diet with 0.4%ML supplementation),TRPC diet(RPC diet with 0.4%ML and 1%taurine supplementation),PRPC diet(RPC diet with 0.4%ML and 0.01%protease supplementation)and CRPC diet(RPC diet with 0.4%ML and 2%CMH supplementation).Weight gain,specific growth rate,protein efficiency ratio and nitrogen and energy utilization of fish fed FM diet were all significantly higher than that of RPC group(P<0.05),but showed no statistical difference with that of the other treatments(P>0.05).Additionally,fish fed RPC diet showed shorter villi length of distal intestine than that of other groups(P<0.05).Furthermore,no significant difference was found in whole-body composition and hepatic and intestinal cell proliferation among all treatments(P>0.05).Otherwise,fish fed RPC diet obtained relatively low mRNA levels of GH,growth hormone receptor,IGF-I,TOR and ribosomal protein S6 kinase 1(in liver,intestine and muscle),myoblast determination protein,myogenic factor 5 and MSTNa(P<0.05),but high expressions of eukaryotic translation initiation factor 4E-binding protein 2(4E-BP2)(in liver and intestine)than that of the other groups(P<0.05).Furthermore,no significant difference was found in 4E-BP2,myogenin,muscle-specific regulatory 4 and MSTNb in muscle(P>0.05).Overall,these results showed that RPC supplemented with ML or CMH could replace fishmeal completely without any adverse effects on growth performance,intestinal morphology and hepatic and intestinal cell proliferation for blunt snout bream.