Study On The Dietary Inclusion Of Pacific Krill Hydrolysates And Whole Fish Hydrolysates Of Lateolabrax Japonicus

In this study,an important cultured fish in China of Japanese seabass(Lateolabrax japonicus)as experimental object,the evaluation of two new marine protein(Hydrolysate of Pacific krill,HPK;Hydrolysate of whole trash-fish,FH)replace Japanese seabass expanded feed medium quality fish meal effect.All the experimental diets were isonitrogenous and isoenergetic were prepared(crude protein 42.6%-43.9%,total energy 19.9-20.4MJ/kg).Control was Peru advanced steam fish meal feed(20%)and soy protein concentrate(10%)as the main protein source,the other 7 kinds of experimental extrusion feed respectively adopts the HPK and soy protein concentrate(SPC,dry base ratio of 1:1)compounds,FH and soy protein concentrate(dry base ratio of 1:1)complex alternative control diet fish meal,substitution level was 25%,50%,75%,100%and 25%,50%,75%,named HPK-25,HPK-50,HPK-75,HPK-100,FH-25,FH-50 and FH-75.A 14-week aquaculture experiment(10 weeks breeding experiment,four weeks digestibility test;initial fish weight 156g)was conducted in RAS.Assess the HPK/FH composite SPC in the different level of the Japanese seabass FI,WG,WGR,SGR and FCR,whole fish composition,protein/energy rate and the apparent digestibility of nutrients,and the experimental group of small peptide transporters(PepTl)gene expression and the influence of liver transcriptome do further analysis,so as to confirm two hydrolysate in Japanese seabass feed the best replacement level,for they spend bass feed in Japan to provide theoretical basis for the application.The research contents and main research results of this paper are as follows:1.Effects of pacific krill hydrolysates and whole fish hydrolysates on feeding growth and feed utilization of Japanese seabassCompared with the control diet,the HPK diets had no significant effect on the WG,WGR,FCR and SR(P>0.05),but the 50%substitution group(HPK-50)had the highest FI and was significantly higher than the 75%and 100%substitution diet(P<0.05).FH diets had no significant effect on the FI,WG,WGR,FCR and SR of Japanese seabass(P>0.05).However,with the increase of substitution level,both FI and WG showed a gradual increase trend,while the FCR showed a gradual decrease trend.Within the range 25%to 75%of the alternative with the pacific krill hydrolysate or whole fish hydrolysate instead of fish meal,respectively,for the Japanese seabass feeding and growth had no significant influence(P>0.05),but using a whole fish hydrolysate has better feed conversion efficiency,FCR to significantly below the Pacific krill hydrolysate compound(P<0.05).2.Effects of Pacific krill hydrolysates and whole fish hydrolysates on composition,accumulations rate and apparent digestibility of feed nutrients.In this experiment,the dry matter,crude protein,crude fat,ash and protein,energy storage rates of all the fish in the HPK diets and the FH diets showed no significant difference compared with the corresponding content of the control diet(P>0.05),The fish crude protein content of HPK-25 was significantly higher than that of HPK-75,HPK-100 treatment diets(P<0.05).But the crude fat content decreased with the increase of substitution ratio.The hepatosomatic index(HSI)of Japanese seabass in the HPK diets and FH diets ranged from 1.7%to 2.5%,and the HPK-25 diet was significantly lower than the control diet(P<0.05),showing the minimum value.The visceral index(VSI)of HPK diets and FH diets showed a range of 16%-19%,and the HPK diets treatment group showed an upward trend with the increase of the replacement ratio HPK-75 had the largest proportion of the HPK diets,and the difference between the treatment diets and the Control diet were no significant(P>0.05).The condition factor range of fish were 16%-18%,and there was not significant difference between each treatment diets and the control diet(P>0.05).The apparent digestibility of crude protein in the HPK diets were significantly higher than the control group(P<0.05),and the HPK-100 diet had the maximum value There was no significant difference in energy and total amino acids apparent digestibility between each treatment diets and the control diet(P>0.05).FH diets and control diet were not significant(P>0.05)In addition to the significant differences in total cholesterol(CHOL)content in the HPK diets(P<0.05),there were no significant differences in ALT,AST,total protein(TP),triglyceride(TG),and high-density lipoprotein(HDL-C)in the whole fish serum(P>0.05).There was no significant difference between the FH diets and the control group(P>0.05).3.PepT1 cDNA sequence analysis of Japanese seabass and the effects of Pacific krill hydrolysates and whole fish hydrolysates on PepT1 expressionIn this study,RACE technology was applied to clone the full-length sequence of PepT1 cDNA(accession no:MK618514)in Japanese seabass.The total length was 3118 bp,including 114 bp 5 ’UTR,817 bp 3’ UTR and 2187 bp open reading frame(ORF),encoding 728 amino acids.TMHMM 2.0 predicted that PepT1 of Japanese seabass contains 12 transmembrane structures(TM),with a long extracellular ring between the 9th and 10th transmembrane domains.Real-time fluorescence quantitative results showed that PepT1 was highly expressed in the intestinal tract,especially in the foregut The PepT1 expression of pacific krill hydrolysates and whole fish hydrolysates in the anterior intestine of Japanese seabass showed that the relative expression of PepT1 mRNA in the anterior intestine was significantly increased when the pacific krill hydrolysates compound replacement ratio was 25%compared with the control diet(P<0.05).The relative expression of PepT1 gene in the foregut was significantly reduced(P<0.05)as the replacement ratio continued to increase,i.e.,50%,75%and 100%.The relative expression of PepT1 mRNA in the anterior intestine was significantly increased when the whole fish hydrolysates compound replacement ratio was 25%compared with the control diet(P<0.05).The relative expression of PepT1 in the foregut was significantly reduced when the replacement ratio continued to increase(i.e.,50%and 75%)(P<0.05).The same substitution ratio of the two protein hydrolysates had significant differences in PepT1 gene expression(P<0.05),and the expression level of the whole fish hydrolysate complex treatment diets were significantly higher than that of the pacific krill hydrolysate complex treatment group when the 25%fish meal was substituted.When 50%and 75%fish meal were replaced,the expression of pacific krill hydrolysate complex treatment diets was significantly higher than that of the whole fish hydrolysate complex treatment group(P<0.05).4.Effects of pacific krill hydrolysates and whole fish hydrolysates on the genetic significance of Japanese seabass liver transcriptomeThe results showed that 1298 and 1514 genes were significantly differentially expressed in HPK diets and FH diets treatment groups compared with control(FM)diet,among which 638 genes were up-regulated and 660 genes were down-regulated in HPK diets compared with FM diet.Compared with the FM diet,the FH diets had 620 genes up-regulated and 894 genes down-regulated(P<0.05),|log2FC|>1.There were 31 and 38 significant differences in KEGG Pathway,(P<0.05).There are ten common KEGG pathways were shown in HPK and FH diets.Differentially expressed genes include lipid metabolism,amino acid metabolism,glucose metabolism,energy metabolism,nucleic acid metabolism,polysaccharide biosynthesis,vitamin and coenzyme factors,transcription translation,signal transduction and immunity.The results showed that pacific krill hydrolysates and whole fish hydrolysates discussed in this study could affect the nutrition,metabolic pathway and immune system of Japanese seabass.In general,the HPK complex maximum replaceable 50%of fish meal;FH complex maximum replaceable 75%of fish meal.In addition,compared with the HPK complex,the FH complex has a higher efficiency of feed conversion and performs better than the HPK complex at the 75%substitution level.