Abstract：A bacterial strain was isolated from liver and kidney of diseased channel catfish Ictalurus punctatus showing symptoms of septicemia in Neijiang city, Sichuan province, by traditional pathogen isolation methods in order to define the potential pathogens and disease control methods of the channel catfish. The pathogenicity of the strain was validated by infection test, and identified as Aeromonas hydrophila by morphological observation, physiological and biochemical characterization, and by 16S rRNA and gyrB gene sequence analysis. The antibiotic susceptibility indicated that the strain was sensitive to ofloxacin, norfloxacin, piperidic acid and tobramycin, intermediary to kanamycin, azithromycin and polymyxin B, and resistant to other drugs in the test. The histopathological observation of the diseased channel catfish showed that the diseased was characterized by congestion of hepatic lobular veins, hepatocyte granule degeneration, granular degeneration of hepatocytes vacuolar and even focal necrosis. Extensive congestion and hemorrhage of renal interstitium, lymphocyte infiltration, degeneration and exfoliation of renal tubular epithelial cells were observed in the diseased fish, and reduction in splenic lymphocyte number, congestion and hemorrhage were found as well. Furthermore, there were necrosis and exfoliation of intestinal mucosa and other pathological changes in the diseased channel catfish. It was concluded that A. hydrophila was identified as the pathogen causing the symptoms of septicemia. The findings provided theoretical basis for the prevention and treatment of the disease.
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2020, Vol. 39 
