Sea lice are a major welfare and production challenge in Atlantic salmon farming; the treatments used to control them carry their own welfare costs that must be weighed against the harm of infestation.
Sea lice management presents a genuine welfare dilemma: untreated infestations cause chronic pain and secondary disease, but many treatment methods also cause significant acute welfare harm. Chemical bath treatments expose fish to stressful crowding and chemical challenge that produces mortality in weakened individuals. Freshwater treatments cause osmotic stress. Mechanical removal using lasers or pumping systems causes physical stress from handling. Cleaner fish — biological control agents added to pens to eat lice — have their own welfare needs that are often poorly met. The welfare calculus requires honest assessment of which treatment approach delivers the best overall welfare outcome across the life of the population, rather than selecting methods based purely on production convenience or lice reduction efficacy without welfare consideration.