ATLANTIC HERRING SHOWS HIGH MORTALITY RATE IN BATH CHALLENGE WITH VIRAL HAEMORRHAGIC SEPTICAEMIA VIRUS (VHSV)

Earlier investigations have demonstrated the presence of viral haemorrhagic septicaemia virus (VHSV) in European herring Clupea harengus in the North Sea, Baltic Sea, English Channel, Skagerrak and Kattegat. Most of the approximately 100 VHSV isolates included in the www.fishpathogen.eu database are of genotype Ib, four are of genotype II and one is of genotype III (4P-168). VHSV is also well known in Pacific herring Clupea pallasii where genotype IV have been detected both in diseased and healthy wild herring. Challenge trials with genotype IV isolates in Pacific herring in the US have shown high mortality rates, while no VHS challenge trials have earlier been conducted on European herring. High prevalence of VHSV genotype Ib was detected in Norwegian spring spawning herring during the spawning season (Johansen et al 2013). The sampled herring showed no signs of disease and were caught by commercial trawl boats. High amounts of virus was found in internal organs (heart, kidney, spleen and brain) showing a septicaemia. How this virus affects the herring stock is unknown. A bath challenge trial with one of these isolates from Norway (NO-F/2009) was conducted on Atlantic herring of approximately 3 gram. In addition herring was challenged with a genotype III isolate from herring (4p168). The Norwegian Ib isolate from herring gave an accumulated mortality of 47% compared to 6% morality with the genotype III isolate. Results from histopathology, immunohistochemistry, RT-PCR and cell culture will be presented. How severely VHSV affects wild stocks of herring in the Northern European waters, and which threat VHSV in wild fish represents to farmed fish are two of the main questions that need to be further investigated. Johansen et al. 2013 "High prevalence og viral haemorrhagic septicaemia virus (VHSV) in Norwegian spring-spawning herring" Marine Ecology Progress Series 478: 223-230