Abstract:[Objective] A continuous high mortality of Carassius auratus gibelio occurred in a farm of Yangzhou area in Jiangsu Province. [Methods] A purely cultured strain (YZ-1) isolated from liver of sick Carassius auratus gibelio, and its main morphological physiological and biochemical characteristics were examined. [Results] For further confirmation on molecular level, 16S rRNA gene was sequenced; and the accession number in GenBank is JX164202 in length of 1 446 bp. Sequences analysis on the 16S rRNA gene shows that it is very similar to other Aeromonas salmonicida, and their nucleotide homology was between 99% to 100%. Its phylogenetic tree showed that the pathogen isolated from the diseased C. auratus gibelio was identified as Aeromonas salmonicida subup. salmonicida isolate. The challenge test using YZ-1 displayed that the prevalence of symptoms and spontaneous onset symptoms were the same. The antibiotic sensitivity using 44 antimicrobial agents showed that the isolate was sensitive to 23 agents, including cefuroxime, cotrimoxazole, enrofloxacin, and cephradine; sensitive slightly to 11 agents, including amikacin, tetracycline, norfloxacin, spectinomycin, and cefradine; and resistant to 10 agents, including peillin G, streptomycin, gentamicin, florfenicol, and vancomycin. [Conclusion] The death of Carassius auratus gibelio is caused by Aeromonas salmonicida subup. salmonicida.
