Rainbow trout is one of the most studied farmed fish species from a welfare perspective. The evidence base for trout welfare informs broader aquaculture standards and highlights both the progress made and the gaps that remain.
Rainbow trout welfare has benefited from a relatively strong evidence base that has translated into some of the better-developed aquaculture welfare standards. The scientific case for trout sentience is robust — trout demonstrate prolonged responses to pain stimuli including rubbing the affected area and reduced feeding that persist beyond the initial stimulus, inconsistent with a simple reflex. Welfare problems in commercial trout farming are well-characterised: fin erosion rates are a practical welfare indicator, with high fin erosion rates indicating crowding, aggression, or poor water quality. Cataract prevalence — caused by deficiencies in specific amino acids in feed — is another measurable welfare outcome that should be monitored. Slaughter welfare improvements have been driven by research demonstrating that trout slaughtered without prior stunning show prolonged brain activity consistent with conscious processing.