Sea lice are the primary disease challenge in Atlantic salmon farming. Treatments range from relatively benign to highly stressful, with significant welfare implications.
Sea lice control creates welfare problems at multiple levels: the lice infestation itself causes suffering, but many treatments are themselves painful or stressful. Mechanical treatments involving fish pumping, laser exposure, and sudden thermal or salinity changes cause measurable physiological stress, scale damage, and behavioral indicators of pain. The cleaner fish approach — using wrasse and lumpfish to consume lice — transfers welfare problems to a different species, with the cleaners themselves experiencing high mortality, aggressive interactions, and the same disease challenges as salmon. The most welfare-positive solutions involve prevention rather than treatment: deep-submerged net pens, snorkel barriers, and selective breeding for lice resistance reduce infestation pressure. The industry has been pushed toward non-chemical approaches that unfortunately include highly stressful mechanical options.