Slaughter methods for farmed fish vary enormously in humaneness, with evidence showing that commonly used methods cause prolonged suffering.
Fish slaughter welfare represents one of the most significant unaddressed animal welfare issues numerically. The practice of leaving fish to suffocate in air or die slowly in ice slurry causes prolonged conscious suffering that would not be acceptable if applied to any other vertebrate animal. Fish cardiovascular and neural systems remain active for many minutes after removal from water, during which nociceptive processing of injury and hypoxia continue. Evidence from brain activity measurements shows that electrical stunning followed by immediate blood loss produces the most rapid loss of consciousness, while CO2 exposure causes active aversion behavior before unconsciousness. The salmon industry in Norway has made significant progress through RSPCA and ASC certification requirements, and large retailers have begun specifying welfare slaughter methods from their suppliers. The scale of fish slaughter means even modest improvements to method adoption affect billions of individuals.