Sea lice (Lepeophtheirus salmonis) infestations cause significant suffering in farmed Atlantic salmon. The welfare implications of different treatment methods — chemical, mechanical, and biological — vary considerably.
Sea lice management in salmon aquaculture creates a welfare dilemma: untreated lice cause chronic suffering, but many treatment methods cause acute additional harm. Chemical and thermal treatments are stressful and can cause physical injury. The welfare calculus requires comparing the sustained harm of lice infestation against the acute but shorter harm of treatment. Welfare-positive management prioritizes prevention through site selection, fallowing, and biological control, reserving treatments for when necessary and choosing the least stressful effective option. Laser and biological methods represent meaningful welfare advances over chemical and thermal treatments.