Evolutionary Changes Of Intestinal Flora And Environmental Adaptations During The Fry Rearing Process Of Acrossocheilus Fasciatus

The growth and development of fish are closely related to their intestinal flora,and the construction of intestinal flora is also closely related to environmental bacterial microorganisms.At present,there is a lack of reports on the evolution of gut flora of freshwater fishes and its correlation with the bacterial microorganisms in the culture water during the nursery period.In this study,we systematically investigated the evolution of the gut flora of A.fasciatus,a stream freshwater fish,during the fry rearing process,to reveal the composition,structure and evolution mechanism of the gut flora with the development of larvae;analyzed the composition and structure of the bacterial community in the culture water of A.fasciatus during the fry breeding process,and elucidated the correlation between the construction of the gut flora and the bacterial microorganisms of the culture water of the fry.We also studied the changes in digestive and immune enzyme activities and the composition and structure of the intestinal flora of the juvenile A.fasciatus in the indoor cement pond and outdoor pond culture environments,and elucidated the physiological responses of the A.fasciatus and the habitat adaptation of its intestinal flora under the habitat differences;compared the changes in digestive and immune enzyme activities and the composition of the intestinal bacterial community of the A.fasciatus before,during and after overwintering,to reveal the adaptive response strategies of the overwintering environment of the A.fasciatus.The specific results are as follows:1.16S rRNA high-throughput sequencing was used to systematically study the composition of the intestinal flora of larval and juvenile A.fasciatus and its correlation with the bacterial community in the culture water during the same period.The results showed that the dominant phyla in the intestinal flora of larval A.fasciatus were Proteobacteria,Bacteroidetes and Firmicutes,and the dominant phyla in the culture water during the same period were Proteobacteria;the dominant phyla in the intestinal flora of juvenile A.fasciatus were Bacteroidetes and Proteobacteria,and the dominant phylum in the culture water during the same period was Proteobacteria,Bacteroidetes and Fusobacteria.Linear regression analysis revealed that the changes of relative abundance of Proteobacteria,Firmicutes and Fusobacteria were consistent in the A.fasciatus and culture water.At the genus level,the dominant genus in the intestinal flora of larval fish was Acetobacter,while the dominant genus in the intestinal flora of juvenile fish was Cetobacterium.Rare and conditionally rare bacterial groups were the main bacterial taxa in the gut flora and bacterial community of the culture water.The correlation analysis showed that the correlation between the gut flora of A.fasciatus and the bacterial community composition of the cultured water body was not significant(P>0.05).2.To study the physiological changes and the adaptation of the gut flora of A.fasciatus under the difference between indoor cement pond culture environment and pond culture environment.The results showed that the intestinal α-amylase in the pond culture environment was significantly higher than that in the cemented pond culture environment(P<0.05);the activities of alkaline phosphatase(AKP),acid phosphatase(ACP)and superoxide dismutase(SOD)in the intestinal tissues of the A.fasciatus in the pond culture environment were significantly higher than those in the indoor cemented pond culture environment(P<0.05).There were no significant differences in the height and width of intestinal villi and intestinal wall thickness between the two culture environments(P>0.05).The results of PcoA analysis and ANOSIM analysis showed significant differences(P>0.05)in the composition of the gut flora of the two culture environments of A.fasciatus.The dominant phyla in the intestinal flora of A.fasciatus in the two culture environments were Proteobacteria,Firmicutes,Actinomycetes and Fusobacteria;the relative abundance of Proteobacteria was significantly higher than the other dominant phyla(P<0.05).The dominant genera in the intestinal tract of the fish in the cement pond culture environment were Ralstonia,Aeromonas,Prevotella and Cetobacterium;the dominant genera in the intestinal flora of the A.fasciatus in the pond culture mode were Neisseria,Ralstonia,Prevotella and Aeromonas.3.This experiment investigated the physiological changes and the effects on the composition of the gut flora of A.fasciatus before,during and after overwinter in a pond culture environment.The results showed that the intestinal α-amylase and lipase activities were significantly higher in the pre-winter than in the post-winter gut of A.fasciatus.The activities of acid phosphatase,superoxide dismutase and catalase(CAT)were the highest in the intestinal tract of the overwintering A.fasciatus(P<0.05).There was no significant difference in the α-diversity index of intestinal flora of A.fasciatus before,during and after overwintering(P>0.05).The results of PCoA and ANOSIM analyses showed significant differences in the composition of A.fasciatus intestinal flora between before and after overwintering(P<0.05).The dominant phylum of the intestinal flora of A.fasciatus before,during and after overwintering consisted of the phylum Proteobacteria,Bacteroidetes,Firmicutes and Actinobacteria,with the relative abundance of Proteobacteria being significantly higher than the other dominant phylum(P<0.05).Ralstonia,Neisseria and Prevotella were consistently present as the dominant genera in the intestinal tract of A.fasciatus before,during and after overwintering.