Application Of Soybean Enzymatic Hydrolysis Protein In Feeding For Largemouth Bass Larvae And Juveniles

Study 1: This study was conducted to investigate the effects of replacing fish meal with mixed plant protein on growth,antioxidant capacity and gene expression related to protein metabolism of largemouth bass(Largemouth bass)larvae.Fish meal was replaced by a mixture of soybean protein(SPH)and vegetable protein(corn protein and fermented soybean meal)with different gradients.Fish meal contents were 40%(FM40),35%(FM35),30%(FM30)and 25%(FM25),respectively,to prepare 4 isonitrogen(crude protein content,51%)and isofat(crude fat content,25%)feed.A total of 480 vigorous fish with the same size and specification(initial body weight 5.05 ± 0.02g)were randomly assigned to 12 culture barrels(capacity 1000L),and 4 experimental groups were set up,with three parallel fish in each group.Satiety was fed twice a day(8:00 and16:00),and the culture experiment period was 10 weeks.The results showed that no negative effect was produced on the growth performance when the proportion of replacement fish meal was less than 10%.At the same time,SPH and plant protein mixture substituted fish meal significantly decreased the content of MDA in liver(P <0.05),and the total antioxidant capacity(T-AOC)and superoxide dismutase(SOD)activities in FM35 and FM30 groups were increased.The expression of genes related to amino acid metabolism in muscle showed that the expression level of LAT1 gene in FM35 was significantly higher than that in control group(P < 0.05),while the expression level of LAT1 gene was decreased in FM30 and FM25 groups,but there was no significant difference compared with control group(P > 0.05).4EBP1 and S6 genes are key genes in the TOR signaling pathway.After SPH combined with plant protein replaced fish meal,the expression level of 4EBP1 gene in all groups was decreased compared with the control group,while the expression level of S6 gene was significantly increased in FM35 and FM30 groups(P < 0.05).In conclusion,it is feasible to replace fish meal with less than 10% of soybean enzymolytic protein and plant protein in combination,which will not have negative effects on the growth of juvenile largess bass,improve the antioxidant capacity of fish and the expression of amino acid transporter LAT1 gene to a certain extent,and have certain activation effects on TOR pathway.In this study,the application of soybean enzymolysis protein in the feed of largemouth bass(Largemouth bass)provides certain data basis for healthy breeding and accurate and efficient development of complex feed.Study 2: This study was conducted to investigate the effects of replacing fish meal with soybean enzymolytic protein on growth performance,digestive enzyme activities and protein metabolity-related gene expression of largemouth bass larvae.Five kinds of isonitrogen(62% crude protein)and isofat(15.24% crude fat)diets were prepared with0%,5%,10%,15% and 20% fish meal replacement(SP0,SP5,SP10,SP15 and SP20),respectively.Fish fry with high vitality and uniform size(initial body weight 13.70 ±0.10mg)were selected and randomly allocated to 15 culture barrels(600L capacity)with 5 experimental groups,3 parallel in each group,and 1000 fish fry per barrel(15days of age).Apparent satiety was fed four times a day(6:00,10:00,14:00,18:00),and the breeding cycle was 28 days.The results of this experiment showed that the specific growth rate and final body weight of largemouth bass larvae in each group were linearly increased with the increase of replacement fish meal ratio compared with the control group(P < 0.05),indicating that it had a significant promoting effect on the growth of largemouth bass larvae.There was no significant change in survival rate among all groups compared with the control group(P > 0.05).When different supplemental levels of soybean enzymolytic protein replaced fish meal,the crude protein content of the whole largebass was linearly increased(P < 0.05),and the activities of lipase,amylase and alkaline phosphatase in the intestine of largebass and juvenile larvae were linearly increased(P < 0.05).After replacing fish meal with soybean enzymolysated protein,there was no significant difference in the gene expressions of amino acid transporters LAT1 and LAT2 in intestinal tract among all groups(P > 0.05),and both were lower than those in fish meal group.However,with the increase of substitution ratio,the expression levels of both genes showed an increasing trend.The addition of enzymolysis protein promoted the expression of small peptide transporter Pep T2 gene,which reached the highest level in SP10 group.The expression of LAT1 gene in muscle was lower than that in control group,and the expression of LAT2 gene in muscle was linearly inhibited after fish meal replacement(P < 0.05).There was no significant difference in the expression level of the small peptide transporter Pep T2 gene among all groups(P > 0.05).The specific regulatory mechanism needs to be further studied.After replacing fish meal with soybean enzymolytic protein,TOR gene expression was linearly increased(P < 0.05),while AKT gene expression was down-regulated.As a downstream effector of TOR pathway,the expression level of S6 gene was linearly increased with the increase of the replacement amount of soybean enzymolytic protein(P < 0.05).In addition,soybean enzymolytic protein significantly down-regulated the expression of e IF2α(P < 0.05).The expression of REDD1 gene,a downstream factor of AAR pathway,was also linearly inhibited(P < 0.05).In conclusion,the replacement of fish meal by soybean enzymolysis protein can activate TOR pathway while inhibit AAR pathway response,promote protein synthesis,and promote the growth of largeus bass larvae.This study provides a theoretical basis for the preparation of artificial microparticle feed for largemouth bass larvae.