Sea lice infestations are treated with chemicals including hydrogen peroxide and emamectin benzoate. These treatments carry significant welfare costs for the salmon and are becoming less effective due to resistance.
Sea lice treatment represents a welfare dilemma: untreated lice cause severe chronic suffering, while treatments cause acute stress and risk mortality. The welfare calculus depends heavily on treatment method, fish condition and the severity of infestation. Chemical treatments involve crowding, handling, chemical exposure and temperature shock in sequence - any one of these is stressful; all together they represent a significant welfare event. Investment in prevention (genetics, lower density, closed containment) and non-chemical alternatives reduces the frequency and severity of these unavoidable welfare costs.