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The microbiota of the intestine produces a wide array of biologically active molecules and together act as a composite endocrine organ. Due to our limited understanding of bacterial communities in aquaculture ecosystems, it is necessary to evaluate the interactions between environmental and intestinal microbiota and the potential consequences of disease. This study taken the traditional P. clarkii culture in the Sichuan Basin as an example, and analyzed the relationships between the microbiota of the environment and host through microbial analysis and microbiological diagnosis. Our results showed that the bacterial abundance in sediment was greater than in water, followed by the intestine, and some of bacteria from the environment successfully selected to colonize the intestine. The bacterial composition in the intestines of diseased and healthy crayfish was significantly different. The bacteria that colonized and proliferated in the intestine had very low abundances in sediment and water. Two potential pathogens, Aeromonas veronii , and Citrobacter freundii , and two potential probiotics, Lactococcus garvieae and Exiguobacterium undae , were identified. Using multiple, real, and traditional P. clarkii aquaculture sites in the Sichuan Basin, this study revealed that the microbial communities of the environment and animal host did indeed interact. Furthermore, these results indicated that P. clarkii in a healthy status are capable of regulating which bacteria colonize their intestines. • The bacterial abundance in sediment was greater than in water, followed by the intestine. • Two bacteria species, L. garvieae and Exiguobacterium , dominated the healthy intestines. • C. bacilloplasma , A. veronii , Citrobacter , and RSAHF231 , were dominant in diseased intestines. • Similar microbial community were found in the Sichuan Basin • A. veronii and C. freundii were isolated from parenteral sites of diseased P. clarkia. [ABSTRACT FROM AUTHOR]

In 2019, an epidemic of ulcerative lesions emerged in grass carp (Ctenopharyngodon idellus) in the Yangtze River basin of China. Diseased fish displayed hemorrhagic ulcers of the tail muscle and reach 70% cumulative mortality, causing serious economic losses. The objective of the present study is to describe disease characteristics, analyze disease factors, and elucidate the etiology. Diseased fish from Qingbaijiang and Deyang, Sichuan, were dissected for the necropsy, pathology, and microbiology investigation. The histopathological examination revealed that the target organs of grass carp were muscle, spleen, and kidney, all showing severe necrosis and varying degrees of inflammation and edema. There were slight changes in the intestine, liver, gill, and heart. Nine strains of bacteria were isolated from diseased grass carp and were identified as belonging to four Aeromonas species. Subsequently, symptoms of tail muscle hemorrhage similar to the clinical symptoms were duplicated through re-infection. There was also a period of low temperatures in the affected regions in the early spring of 2019. Based on the results, we concluded that the genus Aeromonas was the pathogen causing the grass carp epidemic ulcerative disease, which perhaps links to the temperature abnormality. • An epidemic emerged in grass carp with ulcerative lesion was studied. • Inferred to be an infectious pathogenic disease by pathological studies. • Nine strains of bacteria were isolated and identified as genus Aeromonas. • The similar symptoms to nature were duplicated by the re-infection. • The epidemic perhaps links to the continuous low temperature. [ABSTRACT FROM AUTHOR]