The welfare of fish at slaughter varies dramatically between methods, with percussion stunning, electrical stunning, and spiking providing rapid loss of consciousness compared to carbon dioxide or bleeding without stunning.
Fish slaughter welfare is a significant gap between scientific knowledge and commercial practice. Carbon dioxide narcosis — the most common method — is now understood to cause aversive responses before unconsciousness: fish exposed to CO2 show strong avoidance behaviour and physiological indicators of distress. Percussive stunning — a precisely delivered blow to the skull — causes rapid, irreversible loss of consciousness when applied correctly. Electrical stunning in water is effective for salmonids at appropriate current parameters. The gap between the best available methods and routine practice in commercial fish processing represents preventable suffering at a scale of billions of animals annually.