Abstract

The Asian swamp eel ( Monopterus albus ) is an economically vital species in the Chinese aquaculture industry. However, outbreaks of the hemorrhagic septicemic disease caused by Aeromonas veronii have led to substantial economic losses in Asian swamp eel culture and its pathogenesis remains poorly understood. Therefore, this study isolated a pathogenic bacterial strain from diseased fish, which was identified as A. veronii and named the strain MaAv001 through phenotypic and 16S rRNA sequencing analyses. Artificial infection confirmed its high pathogenicity, with an LD 50 of 4.12 × 10 4 CFU/g. Histopathological analysis revealed systemic damage, renal necrosis, splenic lymphocyte reduction, hepatic necrosis and intestinal sloughing. Virulence gene profiling identified six factors ( aer , lip , gcaT , ser , alt , act ) contributing to pathogenicity. The 16S rRNA of intestinal microbiota analysis revealed significant dysbiosis in the intestinal microbiota, marked by reduced beneficial Sphingomonas diversity and increased abundance of Vibrio . Non-targeted metabolomics identified 646 differential metabolites enriched in sulfur relay, glutathione, seleno-compound and cytochrome P450 pathways. This study elucidates the molecular pathogenesis of A. veronii as a primary pathogen of hemorrhagic septicemia in M. albus and its impact on the gut microbiome profiles and metabolomics. These findings provide a theoretical foundation for the diagnosis and prevention of Aeromonas infections in aquaculture.