Sea Lice Treatment in Salmon Aquaculture: Welfare Impacts of Delousing

Sea lice infestations are a major health and welfare challenge in salmon farming, and the treatments used carry their own significant welfare costs.

Key Facts

Sea lice (Lepeophtheirus salmonis) are ectoparasites that feed on salmon mucus, skin, and blood
Heavy infestations cause open wounds, compromised immunity, and death in farmed salmon
Chemical treatments (bath and in-feed medications) have created widespread resistance in lice populations
Thermal delousing uses hot water (34-35 degrees Celsius) to kill lice; the procedure causes significant stress and mortality
Mechanical delousing uses water jets or brushes; associated with scale loss, injury, and death in some fish
Biological control using cleaner fish (wrasse, lumpfish) involves the welfare of two species simultaneously

Welfare Considerations

Sea lice management creates a welfare dilemma: untreated infestations cause severe suffering, but most current treatments also impose significant acute welfare costs. Thermal and mechanical delousing are associated with elevated cortisol, scale loss, injury, and mortality. Chemical treatments reduce lice burdens but create resistance, requiring escalating doses and frequency. High-welfare salmon production requires investment in preventive measures including deep-water feeding systems, single-bay stocking to prevent lice transfer, and site fallowing — approaches that reduce the frequency of interventions needed.

What You Can Do

Support salmon producers investing in preventive sea lice management over reactive treatments
Ask seafood retailers about sea lice management practices on the farms they source from
Advocate for research funding into low-stress sea lice prevention technologies
Learn about the welfare implications of mechanical and thermal delousing when choosing salmon products