Sea lice infestations are one of the most significant welfare and economic challenges in Atlantic salmon farming. Treatment methods vary widely in their welfare impact on fish.
Sea lice treatment creates a welfare dilemma in salmon farming: untreated infestations cause chronic pain and immune suppression, while treatments themselves can cause acute stress and physical injury. Chemical bath treatments require crowding fish into smaller volumes, creating hypoxia and panic responses. Mechanical removal systems cause fin, scale, and eye injuries that introduce secondary infection risk. Cleaner fish represent a lower-stress approach to lice control but themselves face welfare challenges including high mortality rates and inadequate refuges from salmon. The welfare ideal is prevention over treatment: closed containment eliminates sea lice exposure entirely, while selective breeding for resistance and optimized stocking densities reduce infestation pressure in open-net systems.