Survival of Vibrio anguillarum in freshwater environments: adaptation or debilitation?

Vibriosis caused by Vibrio anguillarum seriously damages freshwater fish (Salmoniforms) almost every year in Lake Biwa, Japan. This pathogen requires NaCl for its growth. When the pathogen was exposed to sterilized aged lake water, it lost its culturability without loosing respiratory activity. Although this physiological state appears to be "viable but nonculturable" (VBNC), the cells could not be resuscitated even in host fish bodies. As these cells totally lost their pathogenicity, the VBNC-like state is probably on the pathway to cell death. Environmental factors such as darkness, coldness, and anaerobiosis helped the pathogen to survive in freshwater without reaching a nonculturable state.