Sea Louse Treatment in Salmon Aquaculture: Welfare Impacts (2026)

Sea lice infestations are the primary disease burden in Atlantic salmon aquaculture, with both the infestation and treatment methods causing significant welfare harms to farmed fish.

Key Facts

Lepeophtheirus salmonis is the primary sea louse species affecting farmed Atlantic salmon
Heavy infestations cause severe tissue damage, erosion around the head, and open wounds on salmon
Chemical treatments including azamethiphos bath and hydrogen peroxide bath are physically stressful
Mechanical treatments including the Thermolicer (heated water) and Hydrolicer (pressure) cause thermal and physical stress

Welfare Considerations

Sea lice in heavy infestations cause lesions that breach skin integrity, leading to osmotic stress, secondary bacterial infection, and chronic pain in affected fish. Treatment bath protocols involve crowding fish into confined spaces at high density, causing hypoxia and panic-escape behaviours. Thermal delousing treatments cause elevated fin and scale damage and in some cases fatality. Repeated delousing treatments over a production cycle compound welfare costs. Biological controls (cleaner fish — wrasse and lumpsucker) reduce chemical treatment frequency but raise new welfare concerns for the cleaner fish themselves.

What You Can Do

Choose salmon certified to RSPCA Assured or equivalent schemes with sea lice and treatment welfare monitoring
Support research into non-stressful sea lice management including biological and genetic approaches
Advocate for mandatory welfare assessment of delousing procedures in salmon farming regulations
Raise awareness that sea lice treatment represents a major but often invisible welfare burden in salmon farming