Experimental infection of turbot, Psetta maxima (L.), with strains of viral haemorrhagic septicaemia virus isolated from wild and farmed marine fish
The susceptibility of turbot, Psetta maxima, to infection with two strains of viral haemorrhagic septicaemia virus (VHSV) obtained from wild Greenland halibut, Reinhardtius hippoglossoides, and from farmed turbot was examined. A marine VHSV strain known to be highly pathogenic for turbot was also utilized for comparative purposes. Fish were infected by intra-peritoneal (i.p.), immersion or cohabitation, and maintained at two different temperatures (8 and 15 °C). Infection trials showed that the three VHSV isolates were pathogenic for turbot fingerlings by i.p. injection at both temperatures, with high levels of mortality. Virus was recovered from most pools of dead fish i.p. challenged, but not from surviving fish. Although clinical signs were not induced following waterborne exposure, viral growth was obtained from some pools of surviving fish challenged by immersion with strain GH40 from Greenland halibut, which indicates that the virus can survive in sea water and infect other fish via horizontal transmission. Furthermore, although low, the clinical signs and mortality observed in fish cohabitating with turbot challenged with strain GH40 confirms horizontal transmission and indicates that the passage through fish increases the virulence of this strain for turbot. These findings indicate that Greenland halibut, as other wild fish, may play an important role in the epizootiology of VHSV and suggest a potential risk for the turbot farming industry.