Experimental Infection of Australian Freshwater Fish with Epizootic Haematopoietic Necrosis Virus (EHNV)

The ranavirus, epizootic hematopoietic necrosis virus (EHNV), is endemic to southern Australia with natural outbreaks resulting in mass mortality events in wild Redfin Perch Perca fluviatilis (also known as Eurasian Perch) and less severe disease in farmed Rainbow Trout Oncorhynchus mykiss. To further investigate the host range for EHNV, 12 ecologically or economically important freshwater fish species from southeastern Australia were exposed experimentally to the virus. A bath-challenge model at 18 +/- 3 degrees C was employed with limited use of intraperitoneal inoculation to determine if a species was likely to be susceptible to EHNV. Of the species tested, MurrayDarling Rainbowfish Melanotaenia fluviatilis and Dewfish Tandanus tandanus (also known as Freshwater Catfish) were considered to be potentially susceptible species. EHNV was isolated from approximately 7% of surviving Eastern Mosquitofish Gambusia holbrooki, indicating this widespread alien fish species is a potential carrier. The infection of Silver Perch Bidyanus bidyanus and Macquarie Perch Macquaria australasica and the lack of infection in Murray Cod Maccullochella peelii peelii and Golden Perch Macquaria ambigua ambigua after exposure to EHNV via water confirmed earlier data from Langdon (1989). Five other species of native fish were potentially not susceptible to the virus or the fish were able to recover during the standard 35-d postchallenge observation period. Overall, it appeared that EHNV was less virulent in the present experimental model than in previous studies, but the reasons for this were not identified. Received May 21, 2012; accepted November 1, 2012