The method used to kill farmed salmon at harvest has major welfare implications. Best practice calls for immediate stunning before killing, but practices vary widely.
CO2 stunning causes significant distress - salmon show avoidance behaviour and respiratory distress lasting 30-60 seconds before unconsciousness. Asphyxiation by ice is prolonged and aversive. Well-designed percussion stunning and electrical stunning can render fish unconscious rapidly. Some farms still use live chilling without prior stunning. Industry welfare standards are improving but not universal. Consumer pressure drives faster adoption.