Sea lice treatment in Atlantic salmon farming involves mechanical, thermal, and chemical methods that each carry welfare costs, creating complex trade-offs between pest control and fish welfare.
Sea lice treatment creates an unavoidable welfare dilemma: untreated lice cause chronic pain and mortality, while treatment methods cause acute stress and injury. Thermal treatments can cause scale loss, fin damage, and occasionally gill damage if temperature or duration is poorly controlled. Mechanical treatments risk scale and skin injury. Each treatment event requires crowding, lifting, and exposure to unfamiliar stimuli for fish that show measurable stress responses throughout. The cumulative welfare burden of 10 or more treatment events per production cycle in heavily affected farms is substantial. The welfare-optimal approach prioritises prevention through selective breeding for louse resistance, clean light barriers, and early detection to reduce treatment frequency rather than accepting frequent treatment as routine.