Abstract: The study was carried out to search for the pathogenic factor causing Ornamental carp ulcer disease. A pathogenetic bacterial strain CL0901 was isolated from naturally infected Ornamental carp (Cyprinus carpio L.) in Beijing. The strain was identified according to its physiological and biochemical properties, and the sequence analysis of 16S rRNA gene. The drugs sensitivity was detected with Kirby-Bauer's agar diffusion method. Based on the result of 16S rRNA sequence analysis,the strain CL0901 shares 99.9% sequence identity with the type strain ATTCC 35624T of Aeromonas veronii. Combining with bacteria observation, physiological and biochemical characteristics, the pathogenetic bacterial strain CL0901 was identified as Aeromonas veronii. Drug sensitive tests showed that isolation was sensitive to Neomycin, Piperacillin, Levofloxacin, Norfloxacin, Gentamicin, Amikacin, Tazobactam, Pefloxacin, Lomefloxacin and Tobramycin.

Key words: Ornamental carp; ulcer disease; physiological and biochemical characteristics; sequences analysis of 16S rRNA gene; drug sensitive test