Sea lice treatments in salmon farming cause significant acute stress and injury, making prevention through better farm management more welfare-appropriate than repeated chemical and mechanical interventions.
Sea lice treatment welfare represents a case where every available option involves welfare costs, making prevention the only genuinely welfare-positive approach. Hydrogen peroxide bathing concentrates salmon in tanks with declining oxygen — fish show panic responses, rapid breathing, and increased cortisol. Mechanical delousing using pressurized water causes scale loss and physical trauma that creates secondary infection entry points. Thermal delousing provides the least environmental impact but causes thermal shock stress in salmon. The cleaner fish approach — using wrasse and lumpfish that eat lice from salmon — sounds benign but these species suffer extreme mortality in pen environments: wrasse die from salmon disease, cold temperatures, and predation; lumpfish die from scale damage and stress within months of introduction. Welfare-conscious aquaculture must prioritize site rotation, lower stocking densities, and submerged feeding that reduce lice challenge rather than repeatedly treating heavy infestations.