Identification and Pathogenic Characterization of Aeromonas veronii Isolated from Cultured Amur Catfish (Silurus asotus) in Korea

In March 2025, a mortality outbreak accompanied by skin ulceration, hemorrhage, and corneal opacity occurred in cultured catfish (Silurus asotus) at a fish farm in Jeollabuk-do, Korea. This study aimed to identify the causative bacterium and characterize its pathogenicity and antibiotic resistance. The isolate was identified as Aeromonas veronii based on biochemical and molecular analyses using 16S rRNA and gyrB gene sequences. The isolate exhibited β-hemolysis, gelatin and casein hydrolysis, and carried the virulence genes act and hlyA. It was resistant to tetracycline, oxytetracycline, neomycin, and kanamycin, and the tet(A) gene was detected. Experimental infection by intramuscular injection and immersion reproduced mortality and clinical signs similar to those observed in naturally infected fish, and the same bacterium was re-isolated from infected fish. These findings support the pathogenicity of A. veronii in cultured catfish and suggest its possible enzootic occurrence in catfish farms in Jeollabuk-do.