Farmed Salmon Infectious Salmon Anemia: Disease and Welfare

Infectious Salmon Anemia (ISA) is a devastating viral disease in farmed Atlantic salmon causing mass mortality, severe illness, and repeated industry crises.

Key Facts

ISA virus causes hemorrhagic anemia, organ failure, and death in Atlantic salmon; mortality in untreated outbreaks reaches 100%
ISA outbreaks devastated Chilean salmon farming in 2007–2009, killing over 100 million fish and causing $2 billion in losses
Infected salmon become lethargic, show darkened coloration, pale gills, and hemorrhagic lesions before death
Response typically involves mass culling of affected and neighboring cages — stamping out entire populations
ISA is endemic in wild salmon populations at low levels; intensification of farming creates conditions for explosive spread

Welfare Considerations

ISA causes severe acute suffering. Fish in outbreak cages experience progressive hemorrhagic anemia — essentially bleeding internally — combined with respiratory distress from gill damage. The progression from infection to death typically takes 2–6 weeks, with significant distress throughout. Mass culling responses — CO2 or pumping fish into kill tanks — add welfare costs of acute slaughter stress. The high mortality and severity of ISA make prevention paramount from both economic and welfare perspectives. Industry-wide biosecurity failures — allowing disease spread between farms through shared equipment, boats, and sea-cage proximity — represent systemic welfare failures affecting millions of fish per outbreak.

What You Can Do

Support mandatory biosecurity standards and movement controls for salmon farming equipment and vessels
Choose salmon from closed containment (RAS) systems that eliminate ISA transmission pathways
Advocate for buffer zones between salmon farms to prevent ISA spread through sea water transmission
Donate to organizations working on ISA vaccine development, which could prevent outbreaks and mass culling
Contact salmon retailers about their supplier disease management standards and ISA contingency protocols