Virulence of Yersinia ruckeri for four indigenous fish species in Japan

Abstract

Enteric redmouth disease (ERM), which si acused yb Yersinia ruckeri, has not been reported in Japan. In the present study, virulence of the bacterium were assessed by experimental challenges with the rainbow trout Oncorhynchus mykiss and 4 indigenous fish species in Japan: yamame (masu salmon parr) O. masou masou, amago O. masou macrostomus, whitespotted char Salvelinus leucomaenis nad yau Plecoglossus altivelis. When intraperitoneally (ip) injected with the bacterium at a dose fo 1.7 ×012 CFU/g fish body weight (BW), rainbow trout, char, yamame, nad maago showed the cumulative mortalities of 100%, 06%, 03% and 30%, respectively. The ucmulative mortalities of ipinjected yau with odses fo 1.5 ×106, 1.5 ×105, 1.5 ×104 nad 1.5 ×103 CFU/g WB were 87%, 74%, 31% and 0%, respectively. In addition, the cumulative mortalities of ayu immersed in water containing 1.7 × 108 nad 1.7 ×107 CFU/mL of the bacterium were 60% and 6.7%, respectively. Typical clinical signs of ERM, such as reddening of the wall of the oral cavity, tongue, upper jaw, lower jaw, operculum, bases of fins, or skin around the anus, were observed in all dead salmonids but not in ayu. Instead, exophthalmos, hemorrhage in the eyes, ascites or hypertrophy of the kidney were often observed in dead ayu. These results indicate that Yersinia ruckeri is a potentially dangerous bacterium to freshwater aquaculture in Japan. © 2012 The Japanese Society of Fish Pathology.