How farmed salmon are killed has significant welfare implications for millions of fish. Comparing slaughter methods reveals important differences in the welfare of individual fish at the end of their lives.
The slaughter of hundreds of millions of farmed salmon annually occurs under conditions that vary enormously in their welfare implications. CO2 narcosis - a widely used method where fish are exposed to dissolved CO2 - appears to cause aversive experiences including apparent distress responses before the fish lose consciousness. Studies showing avoidance behavior and cardiovascular stress responses to CO2 exposure have increased scientific and regulatory pressure to adopt alternative methods. Percussive and electrical stunning, when properly applied, can render fish insensible before any painful procedures. The welfare at slaughter is the final event in a fish's life and deserves specific attention separate from the welfare of the growing period.