Sea lice infestations are the most significant health and welfare challenge in Atlantic salmon aquaculture. The treatments used and the infestation itself both have welfare implications that are the subject of ongoing research and regulation.
Salmon lice welfare involves a double burden: the suffering caused by infestation and the suffering caused by treatment. Both require careful assessment. High lice burdens cause measurable physiological stress, immune activation, and behavioral changes. Treatment with mechanical devices causes acute stress, physical injury, and significant post-treatment mortality in some operations. The 'best' welfare approach to lice management is prevention: closed containment systems, strategic farm placement, coordinated area management reducing lice pressure, and selective breeding for lice resistance. None of these are simple solutions, but they address welfare at the system level rather than relying on repeatedly traumatic treatments.