Sea lice are a major welfare and production challenge in Atlantic salmon farming, and treatment methods vary significantly in their welfare implications for both salmon and cleaner fish.
Sea lice treatment creates a welfare dilemma: untreated infestations cause chronic suffering, but many treatments cause acute stress themselves. Thermal delicing causes significant acute distress through rapid temperature change, while medicinal treatments may have sublethal effects on fish physiology. Biological lice control using wrasse cleaner fish transfers welfare concerns from salmon to the wrasse, which suffer cold-water mortality at high rates in Norwegian salmon farms. The welfare-optimal solution involves integrated pest management combining selective breeding, reduced stocking density, and minimally stressful treatment methods rather than reliance on any single approach.