Farmed fish escapes from net pens introduce domesticated fish into wild environments, creating welfare harms for both escaped individuals and wild fish populations through competition, disease transmission, and genetic dilution.
Fish farm escapes create welfare harms at two scales simultaneously. Individual escaped fish experience acute welfare costs: unfamiliar environment, predation pressure without learned avoidance behavior, and competition with more fit wild conspecifics. At the population level, genetic introgression gradually reduces fitness in wild populations, increasing the welfare costs of predation, reduced disease resistance, and poor reproductive success over generations. Improved net pen technology, reduced stocking density to decrease pressure-related net damage, and monitoring programs that detect escapes early enough for intervention represent the most direct welfare-protective responses.