Salmon Delousing Methods and Fish Welfare

Sea lice infestations are a major challenge in Atlantic salmon farming, and the treatments used - from chemicals to mechanical methods - all carry significant welfare risks for fish.

Key Facts

Sea lice are parasitic copepods that feed on salmon skin and mucus, causing lesions and stress
A single heavily infested fish can carry hundreds of lice affecting feeding and immunity
Hydrogen peroxide and azamethiphos are common chemical treatments applied in bath or well-boat
Thermolicer and Hydrolicer mechanical methods use heated water or water pressure to remove lice
Welfare assessments show high acute mortality in some mechanical treatments, especially in weak fish

Welfare Considerations

The welfare implications of delousing are substantial. Chemical bath treatments cause handling stress, oxygen depletion, and potential toxicity. Thermal treatments at temperatures above 34 degrees Celsius cause thermal shock. Mechanical removal causes physical trauma. Farm protocols must carefully assess fish condition before treatment, minimize handling, and choose the method appropriate to fish health status. Preventive strategies including cleaner fish, snorkel barriers, and deep lights reduce treatment frequency.

What You Can Do

Support aquaculture certification schemes that require welfare assessment before delousing
Advocate for mandatory pre-treatment fish welfare scoring on salmon farms
Buy salmon from farms with low lice counts and documented welfare-friendly management
Support research into vaccine-based sea lice control as a non-invasive alternative
Raise awareness about sea lice as a welfare and sustainability issue in salmon farming