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An acute infectious disease of northern sheatfish (Silurus soldatovi) was found in a commercial aquaculture pond in Tianjin, China. Herein, two dominant bacterial strains were isolated from naturally diseased northern sheatfish and identified as Aeromonas veronii and Vibrio cholerae. Seven healthy and seven naturally diseased fish that were collected from the pond were used for the gut microbiota analysis by high‐throughput 16S rRNA gene sequencing. The α‐diversity indices (ACE, Chao 1, and Shannon) did not differ significantly between diseased and healthy fish (p > 0.05), but a significant separation was observed between them when β‐diversity analysis of the bacterial population was performed. The diseased fish demonstrated a significant elevation in the relative abundances of Aeromonas, Vibrio, Blautia, and Megamonas and a decrease in Cetobacterium, Bacteroides, Chryseolinea, Ralstonia, and Pseudomonas compared with healthy fish (p < 0.05). Linear discriminant analysis effect size showed that microbial marker species in the diseased fish were in the order Aeromonadales, the family Aeromonadaceae, and the genus Aeromonas. The functional profiles of the microbial community that were predicted using the PICRUSt2 indicated that the disturbance of gut microbiota caused the alteration of its functional profiles in the diseased fish. [ABSTRACT FROM AUTHOR]

In this study, the delimitation of intestine segments of koi carp (Cyprinus carpio var. koi) was conducted using a histological approach with the measurements of height of mucosa folds (HF), width of mucosa folds (WF), thickness of muscularis (TM) and cross‐sectional area (CSA). According to the change trends for these four parameters, the intestine of the koi carp was divided into anterior intestine, middle intestine and posterior intestine. The locations of the three intestine segments were defined, and their ratios along the entire intestine were accounted for 23.84 ± 1.18%, 46.77 ± 2.29% and 29.39 ± 1.65%, respectively. The anterior intestine had a significantly higher HF, compared with the middle (p <.01) or posterior intestines (p <.01). The muscularis became thin gradually from the anterior intestine to posterior part. TM was significantly different among the anterior, middle and posterior intestines (p <.01). The anterior intestine had a significantly higher CSA, compared with the middle (p <.01) and posterior intestines (p <.01), and the latter two segments had similar CSA values (p >.05). The procedure of the delimitation of the koi carp intestine segments can offer useful information for future studies on other fish species. The presented results are meaningful for studies on differential functions of the different intestine segments in fish. [ABSTRACT FROM AUTHOR]