Larval Pacific herring, Clupea pallasii (Valenciennes), are highly susceptible to viral haemorrhagic septicaemia and survivors are partially protected after their metamorphosis to juveniles

Pacific herring were susceptible to waterborne challenge with viral   haemorrhagic septicaemia virus (VHSV) throughout their early life   history stages, with significantly greater cumulative mortalities   occurring among VHSV-exposed groups of 9-, 44-, 54- and 76-day-old   larvae than among respective control groups. Similarly, among 89-day-  1-year-old and 1+year old post-metamorphosed juveniles, cumulative   mortality was significantly greater in VHSV-challenged groups than   in respective control groups. Larval exposure to VHSV conferred   partial protection to the survivors after their metamorphosis to   juveniles as shown by significantly less cumulative mortalities   among juvenile groups that survived a VHS epidemic as larvae than   among groups that were previously naïve to VHSV. Magnitude of the   protection, measured as relative per cent survival, was a direct   function of larval age at first exposure and was probably a   reflection of gradual developmental onset of immunocompetence. These   results indicate the potential for easily overlooked VHS epizootics   among wild larvae in regions where the virus is endemic and   emphasize the importance of early life history stages of marine fish   in influencing the ecological disease processes.    (VHS); (VHSv); (viral hemorrhagic septicemia); (viral haemorrhagic   septicaemia); (viral hemmorrhagic septicemia)