The method used to kill farmed fish has major implications for their welfare, with many common methods causing prolonged suffering before death.
Fish have nociceptors and show avoidance behaviour to noxious stimuli, suggesting they can experience something like pain. Slow asphyxiation on ice or in air causes prolonged distress. Electrical and percussive stunning cause immediate loss of consciousness when applied correctly but require staff training and equipment investment. The welfare of billions of fish is at stake.