| This study aim at the potential threats to the health of farmed fish using chilled trash fish and the shortage of fishmeal resources,which restrict the healthy development of the aquaculture.The high-quality marine carnivorous fish—hybrid grouper(Epinephelus fuscoguttatus ? × E.lanceolatus ?)as experimental object,focusing on intestinal health,comparing the effects of chilled trash fish and compound feed,and evaluating two plant protein sources(peanut meal,PNM,and low-gossypol cottonseed protein concentrate,CPC)to replace fish meal protein.The specific research contents and results are as follows:1.The fishes were fed with compound feed(FM group)and fish(Harengulazunasi)chilled(CTF group,control group)10-week.The results showed that the growth performance of fish were not significantly different between the groups(P > 0.05).However,bio-economic analysis of the feeds showed that the profit from fish in the FM group was significantly higher than from the CTF group(P < 0.05).The fold height(FH)of the proximal intestine(PI),middle intestine(MI)and distal intestine(DI)and the muscular thickness(MT)of the MI in the FM group was significantly higher than those in the CTF group(P < 0.05).In addition,digestive enzyme(trypsin and pepsin)activities in fish were significantly higher in the FM group,while lysozyme activity was significantly higher in the CTF group(P < 0.05).Levels of complement component 4(C4)and immunoglobulin M(Ig M)in fish serum were significantly lower in FM group fish,while complement component 3(C3)levels were higher in FM group fish(P < 0.05).In the distal intestine,Ig M levels were significantly higher in the FM group,while lysozyme activity and C3 and C4 levels were higher in the CTF group(P < 0.05).The expression of innate immune genes(MHC II ? and TLR22)and inflammatory cytokines(IL-1?,IL-6,IL-10,TNF ?1 and IFN ?)were significantly lower in the FM group(P < 0.05).The bacterial community of the distal intestine was analyzed by Next-Generation Sequencing.At the phylum level,the relative abundance of Acidobacteria was significantly lower in the FM group,while the abundance of Bacteroidetes was lower in the CTF group(P < 0.05).At the family level,the relative abundance of Flavobacterium was significantly lower in the FM group,while the abundance of Bacteroidales S24-7 group and Lachnospiraceae was lower in the CTF group(P < 0.05).The most significantly changed pathways between the two groups were metabolism and genetic information processing(P < 0.05).The overall results showed that feed bioeconomics,intestinal histology,digestive capacity,immunity and intestinal microbiota of fish were superior in the FM group when compared to the CTF group.2.The fishes were fed with the feeds in which fish meal protein was replaced by 0%(FM),10%(PNM10),20%(PNM20),30%(PNM30),40%(PNM40),and 50%(PNM50)PNM 10-week,respectively.The results showed that FM replaced by PNM had no significant effect on the growth performance,feed utilisation,somatic indices,and wholebody composition of hybrid grouper(P > 0.05).Acid phosphatase first became more active and then less active with the increased replacement level(P > 0.05),while the activities of LYS and the contents of Ig M in the intestine were significantly enhanced(P < 0.05).The MHC II ? and TLR 22 expression of DI were significantly up-regulated with the increased replacement rate(P < 0.05).However,there was no significant difference from the FM group with replacement rates of up to 50%(P > 0.05).The m RNA expression of epinecidin and hepcidin of DI in the PNM40 and PNM50 groups was significantly lower than in the FM group(P < 0.05).The gut bacterial community of the DI was analysed by Next-Generation Sequencing.At the phylum level,the relative abundance of Bacteroidetes increased first and then reduced with the increasing rate of replacement,reaching the maximum in the PNM20 group(P > 0.05).At the family level,the relative abundance of Bacteroidales S24-7 group had the same trend(P > 0.05).The relative abundance of Vibrionaceae grew with the increased replacement level,reaching the maximum in the PNM50 group.Functional predictions of the microbiota in DI indicated that the folding,sorting,and degradation pathway was significantly diminished with the increased replacement level(P < 0.05).The glycan biosynthesis and metabolism,and the immune system pathway of the PNM50 group were significantly lower than those in the FM group,while the metabolism of terpenoids and polyketides showed an opposite trend(P < 0.05).In conclusion,replacing FM with PNM of up to 50% had no significant negative influence on growth performance,but obviously changed the immunity and intestinal microbiota of juvenile hybrid grouper.3.The fishes were fed with the feeds in which fish meal protein was replaced by 0%(FM),20%(CPC20),40%(CPC40),and 60%(CPC60)CPC 10-week,respectively.There were 3 repetitions per treatment,and 30 fish per repetition.The results showed that FM replaced by CPC had no significant effect on the growth performance,somatic indices,and whole-body composition of hybrid grouper(P > 0.05).However,the feed conversion ratio of fish in the CPC-containing groups was higher than the FM group,with the significantly higher level in the CPC60 group(P < 0.05).The levels of immunity-related enzymes and gene expression in the fish intestine were also investigated.In the CPC-containing groups,the LYS activity and Ig M levels were significantly increased,while the superoxide dismutase and catalase activities were significantly reduced compared to the FM group(P < 0.05).The m RNA expression of innate immune genes(MHC II ?,TLR22,TNF ?1,IL-6,IFN ?,and IL-10)was significantly increased in CPC-fed fish(P < 0.05)while there was no significant change in the TGF ?1 expression(P > 0.05).The FH and MT of the PI,the MT of the MI and the FH of the DI in the CPC60 group were significantly lower than those in the FM group(P < 0.05).The fold width(FW)of the PI in the CPC20 group was significantly higher than that in the FM group(P < 0.05).The bacterial community in the fish distal intestine was analyzed by Next-Generation Sequencing,which showed no significant difference in alpha diversity between the two diet groups(P > 0.05).At the family level,the relative abundance of Burkholderiaceae was significantly higher in the CPC20 group compared to the FM group,while the relative abundance of Bacteroidales S24-7 group and Lachnospiraceae was significantly higher in the FM group(P < 0.05).The functional prediction of the microbiota indicated that the pathways of amino acid metabolism,xenobiotics biodegradation and metabolism were significantly more abundant in the CPCcontaining groups than the FM group(P < 0.05).In contrast,the pathways associated with genetic information processing(translation,replication and repair)were more prevalent in the FM group(P < 0.05).These results demonstrated that although dietary CPC replacement of levels up to 60% did not significantly alter the growth performance in hybrid grouper,the immune responses were adversely influenced.In addition,replacing FM with CPC had an important impact on microbial profiles but not the diversity.This study shows that there is no significant difference in the growth performance of hybrid grouper fed with chilled trash fish and compound feed;compared with feeding with chilled trash fish,fed compound feed significantly improved the economic benefits,digestive capacity,immune function and intestinal microbiota structure of fish;the appropriate level of PNM and CPC to replace fish meal protein is 30% and 20%,respectively;the replacement of fish meal protein with plant protein upregulate the m RNA expression of intestinal innate immunity and inflammatory factor-related genes;with the increased replacement rate,the relative abundance of beneficial bacteria(Bacteroides S24-7 and Lachnospiraceae)decreased,while the relative abundance of pathogens(Vibrionaceae or Burkholderiaceae)increased. |
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