Sea lice infestations are a leading welfare problem in farmed salmon. Treatment methods themselves carry significant welfare costs that must be weighed against the harm of infestation.
Sea lice management in salmon farming presents a difficult welfare dilemma: infestation causes progressive suffering and mortality, but treatments also cause significant acute welfare impacts. Hydrogen peroxide bath treatments cause stress responses, reduced oxygen uptake, and mortality when misapplied. Thermolicer treatments use water at 34°C — hot enough to kill lice but also close to damaging temperatures for salmon. Cleaner fish used as biological control are themselves poorly understood welfare subjects who die in large numbers on farms. The welfare solution is not any single treatment but rather integrated pest management that reduces infestation pressure through farm siting, density reduction, and breeding for resistance, minimizing the need for stressful interventions.