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Abstract Vibrio vulnificus infections have resulted in great economic losses in intensive aquaculture in China. However, very little was reported on the characterization of pathogenic V. vulnificus strains from freshwater fishes. In this study, a Gram-negative bacterium was isolated from the diseased grass carp (Ctenopharyngodon idellus) and tentatively named strain GCV-515, which was then identified as V. vulnificus by the biochemical characteristics and 16S rDNA, gyrB, CPS and OMP genes sequencing analyses. The pathogenicity of V. vulnificus to grass carp was determined by challenge experiments, and the LD 50 of GCV-515 with intraperitoneal injection was 7.53×103 CFU/g fish weight. Histopathology examination indicated the inflammatory cellular infiltration in submucosa of intestine, venous congestion in liver and necrosis of epithelial cells in the secondary lamella. To our knowledge, this is the first report on the V. vulnificus isolated from the diseased grass carp. Highlights • First report of Vibrio vulnificus infection in grass carp in China. • The phylogenetic analysis showed that the isolate GCV-515 was classified into the genogroup I. • The pathogenicity of V. vulnificus to grass carp was determined by challenge experiments. [ABSTRACT FROM AUTHOR]