Promising Live Vaccine Against Nocardiosis in Japanese Amberjack <i>Seriola quinqueradiata</i>

Trials of several vaccines were conducted to identify a promising candidate vaccine for controlling the infectious disease nocardiosis caused by Nocardia seriolae in Japanese amberjack Seriola quinqueradiata. We investigated the pathogenicity and vaccine efficacy in an indoor aquarium facility with fish weighing 50 to 100 g. A live vaccine using a low-virulence isolate of N. seriolae screened from several N. seriolae isolates derived from infected fish conferred significant protection against the disease. However, neither an inactivated vaccine using formalin-killed cells, ultraviolet-treated bacteria, nor a DNA vaccine encoding the Ag85 gene provided significant protection. Sixty weeks trial demonstrated the long-term effectiveness of the live vaccine. These results indicate that a live vaccine is the most promising approach for controlling nocardiosis in Japanese amberjack.