Disease outbreaks in aquaculture cause mass mortality with severe welfare consequences, and biosecurity measures are the most welfare-effective intervention available.
Disease outbreaks in intensive aquaculture cause mass welfare events affecting millions of individual fish. ISA-infected salmon develop haemorrhagic disease causing progressive organ failure over days to weeks. Emergency slaughter of infected cohorts prevents prolonged suffering but involves stressful collection and killing of fish that may have years of life remaining. Biosecurity that prevents disease introduction is incomparably preferable to emergency response.