1. Fish Health Unit, Marine Institute, Oranmore H91 R673, Ireland
2. Area 52 Research Group, School of Biology and Environmental Science/Earth Institute, University College Dublin, Dublin 4, Ireland
3. The Roslin Institute and Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Midlothian EH25 9RG, UK
4. Marine Scotland Science, Marine Laboratory, Aberdeen AB11 9DB, UK