Challenge studies of European stocks of redfin perch, Perca fluviatilis L., and rainbow trout, Oncorhynchus mykiss (Walbaum), with epizootic haematopoietic necrosis virus

A challenge model for comparison of the virulence of epizootic haematopoietic necrosis virus (EHNV) to European stock of redfin perch, Perca fluviatilis L., and rainbow trout, Oncorhynchus mykiss (Walbaum), was tested. The model investigated intraperitoneal (IP), bath and cohabitation routes at 10, 15 and 20 C for 5–6 g fish and 15 C for 20 g perch.

In the IP challenges of perch, significant mortality occurred at 15 C and 20 C. In challenge trials for rainbow trout, significant mortalities were observed in IP and bath challenges at 20 C. The mortality observed in IP-challenged 20 g perch was not significantly different from that recorded for 6 g fish challenged IP.

No significant mortality was observed in any other treatment groups. Re-isolation of ranavirus was confirmed by IFAT and was con- sistently associated with dead or moribund fish in the trial groups challenged with EHNV. The find- ings indicate that EHNV does not pose a high risk for wild perch and trout populations in Europe by natural exposure.

Mortality appears to be primarily a function of environmental factors, with temperature playing an important role, and not just the presence of the virus in the fish.