The method used to kill fish profoundly affects their welfare — and the commercial fishing and aquaculture industries use methods ranging from humane to severely inhumane at massive scale.
Fish experience pain, fear, and consciousness — the evidence base for this is now substantial. Killing methods that cause prolonged suffocation, ice-slurry asphyxiation, or physical trauma without stunning cause significant suffering. At commercial scale — billions of fish killed annually — the welfare impact of killing method is enormous. Humane killing requires stunning followed by rapid death.