Identification of Two Pathogenic Aeromonas Species Isolated from Juvenile Burbot during Production-Related Epizootics

In response to population declines of North American Burbot Lota lota maculosa (hereafter, Burbot), conservation aquaculture methods have been developed for this species. In general, Burbot are relatively resistant to many salmonid pathogens; however, cultured juvenile Burbot have experienced periodic epizootic disease outbreaks during production. A series of trials was conducted to determine the virulence of select bacteria isolated from juvenile Burbot after outbreaks that occurred in 2012 and 2013 at the University of Idaho's Aquaculture Research Institute. Initial clinical diagnostics and sampling resulted in the isolation of numerous putative bacterial pathogens. To determine which bacteria were the most likely causative agents contributing to these epizootics, juvenile Burbot received intraperitoneal (IP) injections of select bacteria in log-phase growth. Mortality associated with specific isolates was recorded, and more comprehensive challenges followed this initial screening. These challenges used side-by-side IP and immersion methods to expose Burbot to potential pathogens. The challenges resulted in significantly higher mortalities in fish after IP injection with two Aeromonas sp. isolates compared to controls, but no significant difference in mortality for immersion-challenged groups was observed. Results demonstrate that two Aeromonas sp. isolates cultured from the epizootics are virulent to Burbot.