Aquaculture Salmon Social Welfare

Understanding salmon social behavior and addressing social stress is an important but underappreciated dimension of farmed salmon welfare.

Key Facts

Atlantic salmon are not naturally schooling fish and show dominance hierarchies with dominant individuals controlling space and food
In high-density net pens, subordinate salmon experience chronic exclusion from preferred feeding and resting positions
Skin injury scores (measuring fin damage and wounds) are validated welfare indicators of social aggression in salmon populations
Mixing unfamiliar salmon cohorts causes acute aggression as new hierarchies are established
Dimming lights during feeding reduces aggressive competition by reducing visual salience of competitors at feeders
Feeding management including multiple small meals rather than large infrequent feeds reduces competitive aggression
Individual variation in temperament including boldness and stress reactivity affects social success and welfare in group settings

Welfare Considerations

Social welfare in farmed salmon is a dimension that receives less attention than environmental stressors like lice, temperature, and oxygen despite its direct impact on individual fish welfare. The establishment and maintenance of dominance hierarchies in high-density populations creates chronic losers who experience repeated defeat, exclusion from resources, and elevated cortisol that suppresses immune function. Skin wounds from aggressive interactions are welfare indicators that are visible at harvest but rarely assessed during the production period. Management interventions that reduce social aggression include maintaining stable groups without mixing, optimizing feeding distribution to reduce competition, and adjusting light conditions to reduce visual targeting of subordinates. Genetic selection for reduced stress reactivity is emerging as a breeding tool with welfare implications, potentially producing salmon that maintain better welfare in group settings through lower baseline reactivity to social challenges.

What You Can Do

Support salmon welfare research specifically targeting social behavior and social stress indicators in production populations
Advocate for welfare assessment protocols at harvest that include skin damage scoring as an indicator of social welfare during production
Purchase salmon from certified operations that include social welfare management in their standard operating protocols
Support research into genetic selection for calm temperament in farmed salmon to reduce social aggression welfare impacts