REPLICATION OF THE INFECTIOUS SALMON ANEMIA VIRUS (ISAV) IN RAINBOW-TROUT, ONCORHYNCHUS-MYKISS (WALBAUM)

Infectious salmon anaemia (ISA) is a viral disease of farmed Atlantic salmon, Salmo salar L., in Norway. However, in laboratory experiments, the virus has also been found to propagate in trout, Salmo trutta L., where it is a persistent infection. It is crucial for the management of ISA in Norway and for the prevention of spread to fish in other cou ntries, that possible carriers of the virus are found. Another possibl e salmonid reservoir species is the rainbow trout, Oncorhynchus mykiss (Walbaum). After experimental infection, the ISA virus was found to b e present in O. mykiss as late 28 days after infection, with a peak ar ound day 20. The infection resulted in a significant drop in the haema tocrit and haemorrhages on the liver in some specimens. The ISA virus was seen budding from endothelial cells lining blood vessels in the he art ventricle of challenged rainbow trout. It is concluded that the IS A virus is able to propagate in O. mykiss and that this species may fu nction as a reservoir when cultured in areas where the virus is found. The virus does nor seem to cause any significant mortalities of infec ted rainbow trout.