Disease is a major welfare challenge in trout aquaculture. Understanding how production conditions affect disease risk drives welfare-positive management practices.
Disease causes welfare harm through the direct symptoms of infection — lethargy, reduced feeding, behavioral changes, and physical symptoms — as well as through mass mortality events and the stress of treatment operations. High stocking densities amplify disease transmission while simultaneously reducing immune competence through chronic stress. The welfare and commercial interests align here: preventing disease through better management (lower densities, good water quality, vaccination) simultaneously reduces animal suffering and production losses. Antibiotic treatment when required addresses welfare in the short term but creates resistance risks — prioritizing preventive approaches serves both fish welfare and broader public health.