The welfare of farmed Atlantic salmon in the hours and minutes before slaughter is a critical and often overlooked issue, with stunning methods varying widely in their effectiveness at preventing pain.
Pre-slaughter handling involves crowding of salmon into small spaces, which causes stress responses measurable through cortisol levels and behaviour. CO2 is aversive — fish actively avoid it and show opercular movements suggesting distress before losing consciousness. Even approved electrical stunning can fail to produce adequate insensibility if current parameters are incorrect. The transition to fully automated, audited percussive or electrical stunning that consistently achieves immediate insensibility would significantly reduce the suffering of billions of fish annually. Given the sheer numbers involved, even small improvements in stunning reliability represent enormous welfare gains.