The harvesting of farmed finfish including salmon and trout is a welfare-critical event in the production cycle, with the methods used for crowding, stunning, and killing having major implications for individual fish welfare.
Harvest welfare for farmed finfish depends on minimising the duration and intensity of pre-slaughter crowding stress and ensuring immediate and effective stunning before death. CO2 immersion, still widely used, causes fish to avoid the gas and show signs of distress - it is not an appropriate stunning method from a welfare perspective. Electrical water stunning, where fish swim through an electrical field that renders them immediately unconscious, provides a significant welfare improvement and is becoming the gold standard for salmon harvest. Percussive stunning using a blow to the head can be effective but requires careful technique to ensure immediate unconsciousness.