Slaughter methods for farmed fish have significant welfare implications, with CO2 immersion causing distress and alternatives including percussive stunning offering better welfare outcomes.
Fish slaughter welfare is at an early stage of regulatory reform - standards that exist for mammal and poultry slaughter have not been systematically applied to fish despite the billions of farmed fish slaughtered annually. CO2 immersion causes avoidance behaviour and physiological indicators of distress before immobilisation - a better-than-nothing reduction in awareness during slaughter but not a welfare-positive method. Electrical stunning provides rapid loss of consciousness when correctly calibrated for species and size. Percussive stunning works but requires skill and is difficult at scale. Welfare improvement requires investment in species-specific stunning technology and regulation requiring its use, similar to mammal slaughter requirements.