Salmon Lice Treatment: Welfare Impacts of Delousing in Aquaculture

Sea lice are a major health and welfare problem in farmed Atlantic salmon. Treatment methods vary significantly in their welfare implications for the fish.

Key Facts

Sea lice (Lepeophtheirus salmonis) cause tissue damage, stress, and secondary infections in farmed salmon
Thermal delousing uses hot water to dislodge lice and is associated with serious injuries and mortality
Mechanical delousing (hydrolicer) removes lice using water jets and also causes injuries
Biological control using cleaner fish such as wrasse is a lower-stress alternative
Coordination between farms to synchronise fallowing reduces lice pressure without treatment

Welfare Considerations

Sea lice management represents one of the most significant welfare challenges in salmon aquaculture. The parasites cause tissue damage and immunosuppression that impair welfare and survival. However, the most widely used treatment methods — thermal and mechanical delousing — cause their own welfare harms: scale loss, skin injuries, physiological stress, and mortality. Welfare-conscious aquaculture operators are adopting integrated pest management approaches that prioritise biological control, improved husbandry to reduce infestation risk, and selective use of treatments with the best welfare profiles. Cleaner fish provide a lower-stress alternative but have their own welfare requirements that must be met.

What You Can Do

Choose farmed salmon certified to welfare schemes that address lice management
Support research into improved sea lice management methods with better welfare profiles
Advocate for mandatory welfare assessment of delousing treatment methods
Reduce salmon consumption or choose wild-caught alternatives where available