Sea lice are external parasites that cause skin damage in farmed Atlantic salmon. Treatment methods range from chemical to biological and mechanical, each with different welfare implications for salmon and for wild fish populations.
Sea lice management involves unavoidable welfare trade-offs: infestation causes chronic skin damage and pain; treatment also causes acute stress. The challenge is identifying the least-harmful combination of prevention and treatment. Chemical treatments have declining efficacy and their own welfare costs; mechanical treatments (warmwater or freshwater bathing, thermolicers) involve handling and thermal stress; cleaner fish have their own welfare needs that are often inadequately met. Preventive approaches - snorkel barriers, deep lighting, selective breeding for resistance - offer the best welfare profile by reducing the need for reactive treatments. Industry welfare standards should prioritise prevention over reactive treatment cycles.