Sea lice infestations and the treatments used to control them represent one of the most significant and complex welfare challenges in Atlantic salmon aquaculture.
Sea lice management epitomizes the welfare trade-offs inherent in intensive fish farming. Left untreated, sea lice at high densities cause chronic pain through tissue damage — lesions can penetrate to the underlying muscle. Yet the dominant treatment methods each carry their own welfare costs. Hydrogen peroxide baths effectively kill lice but cause oxygen depletion and acute panic responses measurable in cortisol and behavior. Mechanical removal technologies including thermal delousing and laser systems cause startle responses and physical trauma during handling. Even biological control via cleaner fish is problematic — wrasse and lumpfish used as delousing agents suffer extremely high mortality in open-net salmon pens, often dying from stress, disease, and physical injury within months. Welfare-conscious aquaculture requires prevention through lower stocking density and site rotation rather than treating chronic infestations.