The Effect Of Alginate Oligosaccharide On Growth Performance,Physiology And Biochemistry,Gut Microbiota And Liver Transcriptome Of Epinephelus Coioides

A 56-day single-factor feeding trial was conducted to determine the effect of Alginate Oligosaccharide（AlgOS）on the growth performance,nonspecific immunity,antioxidant capacity,gut and liver histology structure,gut microbiota and liver transcriptome of the juvenile grouper（Epinephelus coioides）with initial body weight（50.52±1.05）g and full length（14±0.18）cm,in which the supplement of AlgOS were 0.00%,0.10%,0.20%,0.40%,0.80%,respectively.Also,as a biologically active substance,the study aims to evaluating the potential application of AlgOS and accumulating basic data for it in fish formula feed.The main results of the research are as follows:1.The effect of AlgOS on the growth performance of juvenile grouperAlgOS had no significant effects on the growth performance（SR,WGR,SGR,CF,FCR）and gastrointestinal digestive enzyme（Pepsin,TRY,LPS,AMS）activities of juvenile grouper（P>0.05）.2.The effect of AlgOS on the non-specific immune parameters and transaminase activities of juvenile grouperAlgOS increased the serum AKP,liver ACP and serum and liver LZM activities of juvenile grouper significantly（P<0.05）.In addition,the serum GOT activities decreased significantly（P<0.05）,but have no difference on serum GPT,liver GPT and GOT,even though the latter was increased（P>0.05）.3.The effect of AlgOS on the antioxidant capacity of juvenile grouperMost of the antioxidant parameters including liver T-AOC,GSH-Px,SOD and serum GSH-Px activities were increased significantly（P<0.05）by treating with the different supplementation level of AlgOS.Furthermore,serum and liver MDA decreased significantly（P<0.05）.4.The effect of AlgOS on gut histological structure and gut microbiota of juvenile grouperAlgOS improved the gut histological structure by increasing the MP and MFH of juvenile grouper significantly（P<0.05）and the number of GC.Using a 16S rDNA gene amplicon sequencing technique,it was found that AlgOS remodels the gut microbiota.Alpha diversity increased significantly with 0.20%and 0.40%AlgOS（P<0.05）while with 0.10%and 0.80%AlgOS the alteration occurred without impacting（P>0.05）the bacterial diversity.Beta diversity analysis showed the significant differences between 5 groups（P<0.05）.Furthermore,AlgOS increased the relative abundance of probiotics,including Bifidobacteria,Lactobacillus,and some bacteria related to SCFA production（Ruminiclostridium₁,Christensenellaceae_R-7_group,etc）while inhibited the colonization of harmful bacteria（such as Klebsiella）in the gut of juvenile grouper.5.The effect of AlgOS on liver histological structure and transcriptome of juvenile grouperThere is no difference on the liver histological structure of juvenile grouper among which the liver cells morphology in each group was normal,and there was no nuclear deviation and fat deposition.Through high-throughput sequencing technology,it was found that there are many DEGs related to metabolism and immunity.Moreover,With the increase of AlgOS supplementation,the number of up-regulated genes in the 0.20%group reached a stable level,while the number of down-regulated genes in 0.80%group has increased dramatically.AlgOS regulated gene expression such as gene-related peptide（CGRP）,heat shock proteins（HSPs）,Toll-like receptors（TLR）,Stomatin-like protein 2（STOML2）,fatty acid desaturase（FADs）.Many significantly down-regulated genes are enriched in metabolic pathways（MAPKs,AMPK and NF-κB,etc）.These DEGs and metabolic pathways are related to inflammation,immune response and energy metabolism of juvenile grouper.It was concluded that AlgOS is potential and had a significant effect on the growth performance and physiological and biochemical system,which adversely affected the growth and health of the juvenile grouper.The recommended supplemental level of AlgOS in grouper formula feed is 0.20%～0.40%.