Study On Liver Transcriptome And Intestinal Microbes During The Weaning Of Largemouth Bass In Pond

In recent years,largemouth bass has gradually become one of the most popular and famous breeding species,it also has become the “Fivth” domesticated fresh fish in China.The weaning is the most critical cultivation-operation for largemouth bass aquaculture.However,it is obviously that low survival rate of larvae has always restricted the development of the industry during weaning stage.In this study,the next-generation sequencing technology was used to reveal the dynamic changes of liver metabolism and intestinal microbiome of largemouth bass during the weaning process,and to determine the digestive capacity during the weaning process by measuring the activity of digestive enzymes.The main results are as follows:(1)The differentially expressed genes(DEGs)were analysed among three weaning stages.Compared with the other two weaning stages,156 HEGs(higher expression genes)were and 260 LEGs(lower expression genes)were found in the liver of pre-weaning stage.60 HEGs and 20 LEGs were obtained in mid-weaning stage;206 HEGs and 165 were found in post-weaning stage.(2)In the pre-weaning stage,the enrichment of HEGs were related with cholesterol metabolism,antigen processing and introduction,vitamin digestion and absorption,amino acid biosynthesis and metabolism,protein processing in endoplasmic reticulum,etc;the enrichment of LEGs in fatty acid biosynthesis,PPAR signaling pathway,fat digestion and absorption,protein digestion and absorption,pancreas secretion.The HEGs in the mid-stage were enriched in metabolic pathways such as environmental information processing,protein digestion and absorption,transport,and catabolism;The LEGs were enriched in complement and coagulation cascades,platelet activation,ascorbic acid,and metabolism.The HEGs were enriched in the PPAR signal pathway,unsaturated fatty acid biosynthesis,fatty acid metabolism,carbon metabolism,and protein processing in the endoplasmic reticulum in the post-weaning stage;the LEGs were enriched in amino acid metabolism,amino acid biosynthesis and bile secretion pathways.(3)The intestinal microbes in the three weaning stages were mainly distributed in the Firmicutes,Proteobacteria,Cyanobacteria,Bacteroidetes,Actinobacteria,Tenericutes and Fusobacteria.Among them,the changes of Proteobacteria and Firmicutes were most significant.The abundance of Proteobacteria decreased from 56.32% of pre-weaning stages to 28.91% and 16.84% in the mid-and post-weaning stages,while the abundance of Firmicutes increased from 25.29% to 60.70%,62.81%.The abundances of Plesiomonas,Sphingomonas,Acinetobacter and Stenotrophomonas of Proteobacteria were significantly decreased in the mid-and post-weaning stages,while Clostridium the most significant increase in abundance.(4)It was found that three important digestive enzymes(trypsase,lipase,and amylase)in the intestine had a significant decrease in the mid-weaning stage(p < 0.5).The amylase in the liver showed a downward trend during the weaning process,but lipase and trypsase were not detected in the liver.With the progress of the weaning,the intestine villi height,width,intestinal wall thickness,and intestinal absorption area of the largemouth bass were significantly higher in post-weaning stage.However,the intestinal wall thickness and intestinal absorption area were the smallest in the mid-weaning stage.In general,this study revealed the dynamic changes in liver transcriptome,intestinal microbiome,and intestinal digestive enzymes during largemouth bass weaning,providing a basis and reference for future largemouth bass weaning studies.