The slaughter of farmed fish at scale raises major welfare questions; current methods vary widely in their humaneness and the scientific consensus on best practice.
Fish die slowly during asphyxiation, remaining conscious for minutes during oxygen deprivation. Ice slurry immobilises without rendering fish insensible. Conscious fish being bled or gutted experience pain. Percussive stunning (a blow to the head) provides instant insensibility when delivered accurately, but requires skill and is impractical at very high throughput. Electrical stunning before killing represents the current best practice recommendation for salmon and trout but is not universally applied.