Sea lice treatments in salmon aquaculture carry significant welfare costs that must be balanced against the welfare harm of untreated lice infestations.
Sea lice treatment welfare involves difficult trade-offs. Untreated lice cause progressive tissue damage and welfare harm. But many treatments cause their own welfare problems: crowding salmon to high densities for bath treatments causes hypoxia stress; hydrogen peroxide treatments cause irritation and can be fatal at incorrect doses; thermal treatments cause temperature shock. The emerging concern about cleaner fish welfare adds another dimension - wrasse and lumpfish used to control lice are often kept in poor conditions themselves and have high mortality rates. The welfare-optimal approach minimizes lice burden through prevention (site selection, fallowing, stocking density management), uses the least stressful effective treatment when necessary, and ensures adequate welfare for any cleaner fish used in biological control.