Carbon dioxide stunning of farmed salmon before slaughter is widely used but raises welfare concerns due to aversion and potentially inadequate depth of stun.
CO2 stunning causes a period of apparent distress before unconsciousness in salmon, suggesting that animals are aware and experiencing aversive states during induction. The welfare concern is compounded by uncertainty about the depth of stun achieved. Electrical stunning that delivers immediate insensibility is a higher welfare alternative that is gaining regulatory support. The scale of salmon slaughter - millions of animals annually - makes the welfare significance of stunning method enormous. Progress toward electrical stunning standards represents a major welfare improvement opportunity.