Infectious salmon anemia (ISA) is a viral disease of Atlantic salmon (Salmo salar) caused by Salmon isavirus. It affects fish farms in Canada, Norway, Scotland and Chile, causing severe losses to infected farms.
ISA virus causes severe anemia in infected fish. The fish develop pale gills, and may swim close to the water surface, gulping for air. However, the fish may show no external signs of illness and maintain a normal appetite, until suddenly dying. The disease can progress slowly throughout an infected farm and, in the worst cases, death rates may approach 100%.