Characteristic And Impact Factors Of Fish Intestinal Flora In Anhui Section Of Huai River During Dry Season

The development and utilization activities of Huai River Basin by human beings have become increasingly intensified,according to statistics,64 percentage of rivers in the Huai River Basin are in unhealthy or sub-healthy state;The natural landform has been destroyed and some rivers have been cut off.Water quality is destroyed,water ecosystem disintegrates,biodiversity declines sharply;river fishery resources decline,migratory and semi-migratory fish gradually decrease,and the proportion of small low-value wild fish keeps rising.At present,the research on fish intestinal flora mainly focuses on the composition of intestinal flora of farmed fish,the factors affecting intestinal flora and the research methods of intestinal flora,there are few studies on the composition and influencing factors of fish intestinal flora in a natural environment.In this study,16 SrRNA high-throughput sequencing technology combined with bioinformatics analysis methods were used to detect and analyze the intestinal flora characteristics of 39 species of fish in Anhui section of Huai River during dry season,and 6 species of dominant fish were selected as research objects,they are Acheilognathus chankaensis,Abbottina rivularis,Coilia brachygnathus,Hemiculter bleekeri,Pelteobaggrus nitidus and Parabramis pekinensis.and analyzed the effects of different diets,living water layers and roosting reaches.In order to build a database of fish intestinal flora in Anhui section of the Huai River main stream,explore the potential influencing factors of fish intestinal flora,and provide certain references for fish health and human activities interfering with the ecological problems of the Huai River basin from the perspective of intestinal microecology.The specific results are as follows:(1)Characteristics of fish intestinal flora in Anhui section of Huai River Main StreamA total of 56 phyla and 1959 genera were detected in 39 fish intestinal samples from Anhui section of Huai River.Among them,the dominant phylum is Proteobacteria,Cyanobacteria,Verrucomicrobia,Firmicutes,Actinobacteria,Planctomycetes,Bacteroidetes,Acidobacteria.The dominant genus is mainly Brevundimonas,Pseudomonas,Sphingomonas,Oxyphotobacteria＿unclassified,Acinetobacter,Luteolibacter,Herbaspirillum.The Chao1 index analysis of 39 species of fish shows that there is a large gap between different fish with the highest value of 865.5 and the lowest value of 57.0.(2)Characteristics of intestinal flora of different feeding fishesIn terms of feeding habits,the six species of fish were divided into three groups:herbivorous,ployphagous and carnivorous.The results showed that total and endemic ASVs were the highest in the gut of herbivorous fish.There were significant differences in intestinal flora of different feeding fish(P<0.05),for example,the proportion of xanthobacterium in the gut of herbivorous fish was significantly higher than that of carnivorous and omnivorous fish.LEf Se analysis showed that 46 species of distinctive bacteria existed in the intestinal tracts of herbivorous fish,while carnivorous and omnivorous fish had fewer species(8 species and 4 species,respectively).The common dominant bacterial community in the intestinal tracts of the three feeding fishes was mainly Brevundimonas,Pseudomonas,Oxyphotobacteria＿unclassified,Luteolibacter,Acinetobacter,Curvibacter,However,the relative abundance was different among groups.(3)Characteristics of intestinal flora of fishes in different living water layersIn terms of living water layer,the six species of fish are divided into three groups:bottom,middle and upper layer.The results showed that the number of total and unique ASVs in the intestinal tracts of fish in the middle water layer was the highest.There were significant differences in the composition of fish intestinal flora in different water layers(P<0.05).LEf Se analysis found that the intestinal tract of bottom-layer fish was enriched with 17 species of signature differential bacteria,while that of upper-layer and intermediate layer fish was enriched with 2 species and4 species,respectively.The common dominant flora in the intestinal tracts of the three species of aquatic fish mainly included Brevundimonas,Pseudomonas,Sphingomonas,Oxyphotobacteria＿unclassified,Acinetobacter,Luteolibacter.Among them,there were significant differences between Pseudomonas and sphingosinomonas in the intestinal tracts of fish in different resident water layers.(4)Characteristics of intestinal flora of fishes in different roosting reachesIn terms of habitat reach,the Anhui section of the main stream of the Huai River is divided into three reaches,namely the lower reach,the middle reach and the upper reach,with Linhuaigang Gate and Bengbu Gate as the boundary.LEf Se analysis showed that the intestinal tracts of fish in the middle section were enriched with a large number of signature differential bacteria,such as Enterococcus,Ethanoligenens and Carnobacterium,which they can degrade organic matter and inhibit pathogens,and provide important help for fish to resist water pollution and pathogens.The common dominant flora of fish intestinal tracts in the three river reaches were mainly Brevundimonas,Pseudomonas,Sphingomonas,Oxyphotobacteria＿unclassified,Curvibacter.Different from the feeding group and water layer group mentioned above,the relative abundance of fish intestinal flora in different river reaches had little difference,indicating that the division of water area may not have a great impact on fish intestinal flora in different roosting reaches.In conclusion,based on the overall analysis results of intestinal flora of all species in the surveyed waters,the species richness index and diversity index of intestinal flora of fish in Anhui section of the Huai River were significantly different.Based on the analysis of intestinal microflora detection data of six fish species in key studies,intestinal microflora composition is closely related to feeding habits,habitat water layer and habitat reach,and the influence of feeding habits and habitat water layer on fish intestinal microflora is more significant than that of habitat reach.In the experimental groups set for fish feeding,habitat water layer and habitat reach,there were significant differences between the herbivorous fish,benthic fish and the fish in the middle reach and the other groups.