[A new pathogen of gibel carp Carassius auratus gibelio-Shewanella putrefaciens]

We studied a novel disease occurred among cultured Carassius auratus gibelio at a farm located in Yancheng City, Jiangsu Province.

The dominant bacteria were isolated from diseased fish. The pure culture of the isolated strain was analyzed using conventional physiological and biochemical tests, together with 16S rDNA gene sequencing. An experimental infection of Carassius auratus gibelio with the isolated strain was performed to fulfill the Koch postulates. K-B method was used for antibiotic susceptibility testing.

The causal agent of the disease was finally proved to be one species of bacteria that was identified as Shewanella putrefaciens. Experimental infection with S. putrefaciens resulted in the same gross signs as naturally infected fish and the same bacteria were recovered in a pure culture from freshly dead fish. The LD50 of S. putrefacien was calculated as 2.1 x 10(3) cfu/g. The result of drug sensitivity test showed that S. putrefaciens was sensitive to Pipemidic acid, Nalidixic acid, Fluperacid, Enoxacin, Florfenicol, Rifampicin, Minocycline, Fleroxacin, Enrofloxacin, Ceftriaxone, Cefalexin, Ceftazidine, Roxithromycin and Levofloxacin.

This is the first report on a new pathogen of Carassius auratus gibelio, revealing that S. putrefaciens as a potential new pathogen may pose a threat to the culture of Carassius auratus gibelio.