Pre-slaughter stunning of farmed salmon is increasingly required by welfare standards but implementation varies enormously, and many fish are still killed without effective stunning.
Salmon killed without effective prior stunning experience the killing process while conscious. Gill cutting in conscious fish causes haemorrhage and arousal rather than immediate unconsciousness. Percussion stunning applied incorrectly may stun but not kill, allowing recovery of consciousness during bleeding. Effective stunning followed by immediate killing is achievable at scale and represents a major welfare improvement for billions of fish.