Sea lice infestations cause serious welfare harm to farmed Atlantic salmon, and many of the treatments used to control them also cause significant fish suffering. Finding better solutions is a major research priority.
Sea lice cause chronic pain and distress through direct tissue damage at attachment sites. Secondary infections from lice damage cause additional suffering. Treatment itself is welfare-costly: crowding fish for treatment, mechanical removal, and chemical baths all generate acute stress. Fish subjected to repeated delousing treatments show cumulative welfare deterioration. Biological control using cleaner fish (wrasse and lumpfish) reduces chemical treatment but raises its own welfare concerns about cleaner fish living conditions.