Histopathology of yearling sockeye salmon (Oncorhynchus nerka) infected with infectious hematopoietic necrosis (IHN)

Infectious hematopoietic necrosis (IHN) is generally believed to be a virus disease of very young salmonids. In recent years there have been increasing numbers of unpublished reports that this disease has been occurring uncharacteristically in fish as old as 7-14 months. Sockeye salmon (Oncorhynchus nerka) of this age the histological changes were not severe. Intestinal tract granular cells thought to be pathognomic in young fish were conspicuously absent. Kidney imprints showed necrobiotic bodies however, and subtle changes were observed in the spleen and kidney hematopoietic tissue.