Sea lice infestations are a major welfare and health challenge in salmon farming. Treatment methods vary significantly in their welfare impact on fish.
Sea lice management illustrates the difficult welfare trade-offs in salmon aquaculture. Infestation causes chronic pain and tissue damage; treatment itself imposes acute stress. Thermal delousing exposes fish to sudden temperature changes that cause scale loss and physiological shock. Chemical bath treatments require crowding fish, removing them from water, and exposing them to compounds that may affect nervous system function. Biological control with cleaner fish improves outcomes but raises welfare concerns for the cleaner fish themselves, which often suffer high mortality in salmon cages. Enclosed recirculating aquaculture systems that prevent lice exposure represent the highest-welfare approach, though they require greater capital investment.