Sea lice infestations are a major welfare and production problem in farmed Atlantic salmon. Management approaches vary significantly in their welfare implications for both salmon and wild fish.
Sea lice management represents a welfare dilemma with no perfect solution. Heavy lice burdens cause genuine suffering through tissue damage, osmotic stress and secondary infection. Chemical treatments address the immediate welfare problem but have environmental impacts and increasing resistance. Mechanical treatments including warm water flushes and snorkel barriers expose fish to acute stress. Cleaner fish — deployed to consume lice from salmon — face perhaps the worst welfare outcomes of all: wrasse and lumpfish are caught from the wild or poorly farmed, transported and deployed into conditions where their welfare needs are almost entirely unmet. The most welfare-positive solution for all species involved is land-based closed containment, which eliminates lice infestations entirely, but this remains expensive and not yet mainstream.