Pre-slaughter stunning is essential for humane fish killing. Multiple stunning technologies exist with different welfare profiles, and adoption varies widely across farmed fish species and countries.
Fish stunning welfare is the most acute welfare issue in aquaculture because it affects every individual at the moment of greatest vulnerability. Current widespread practices including CO2 narcosis and ice slurry chilling cause distress before insensibility is achieved. CO2 is actively aversive — fish avoid it and show increased opercular beat and abnormal behavior as CO2 concentration increases before loss of consciousness. Electrical stunning, when correctly calibrated to species, size, and water conductivity, achieves immediate loss of consciousness with minimal distress. Percussion stunning using automated spiking achieves immediate brain destruction. The welfare improvement from transitioning from aversive to effective stunning is large and immediate, making this a high-priority intervention for any welfare-conscious aquaculture operation.