Outbreaks of vibriosis associated with Vibrio mimicus in freshwater catfish in China

An epidemic with a high mortality rate (80%–100%) recently occurred in yellow catfish, southern catfish, and Zhengchuan catfish in China. The clinical and pathological features were similar to those previously described for fish infected with vibriosis. Six bacterial strains were isolated from the different affected catfish species between 2011 and 2013. Based on the phenotypic characteristics, 16S rRNA and gyrB gene sequence analysis, and multiplex PCR detection, all isolated strains were identified as Vibrio mimicus. The hemolysin gene was detected in all of the V. mimicus isolates, whereas none possessed the ctxA, zot, ace, or tcpA gene. The virulence tests were conducted by intraperitoneally injecting the V. mimicus isolates into healthy fish, and the results showed that all of the isolates were lethal to yellow catfish, southern catfish, and Zhengchuan catfish. The challenged fish showed similar clinical symptoms as those that were naturally infected. The results of this investigation indicate that V. mimicus was the causative agent of the natural epizootic. This is the first report of V. mimicus infection associated with mass mortality in freshwater catfish.