Sea lice are the most significant health and welfare challenge in Atlantic salmon aquaculture, and the treatments used to control them — from medicinal baths to mechanical and thermal delousing — raise serious welfare concerns of their own.
Sea lice management in salmon aquaculture creates a painful welfare dilemma: lice cause significant suffering through skin damage and osmotic stress, but many of the treatments developed to control them also cause substantial welfare harm. Thermal delousing at temperatures that dislodge lice is associated with cataracts that permanently impair vision, a significant welfare harm to an animal in which vision matters for schooling, predator avoidance, and feeding. High-density bath treatments cause confinement stress. Cleaner fish — particularly lumpfish — are often poorly cared for and experience high mortality rates, meaning millions of individuals suffer as a tool for managing welfare in another species. The most welfare-positive approaches combine selective breeding for lice resistance, genetic stock selection, and site management to reduce lice pressure rather than relying on repeated harmful treatment.