Sea lice infestations are the primary chronic welfare and production problem in Atlantic salmon farming, with treatments carrying their own welfare costs and environmental spillover effects on wild fish.
Sea lice management represents a welfare dilemma: the infestation causes ongoing pain and tissue damage, while treatments carry their own acute welfare costs. Well-calibrated treatments provide net welfare benefit by removing the chronic pain of infestation, but poorly calibrated treatments cause additional suffering without adequate benefit. Cleaner fish placed in salmon cages to consume lice face their own severe welfare challenges — high mortality rates, inadequate nutrition, insufficient shelter, and stress from the cage environment. Some wrasse and lumpfish show injury rates above 50% in production cage settings. A comprehensive welfare approach to sea lice management must account for both salmon welfare and cleaner fish welfare, pursuing the lowest total welfare cost solution.