Sea lice treatments used in salmon farming — including hydrogen peroxide baths and mechanical delicing — cause significant acute welfare impacts on salmon, raising questions about treatment costs versus parasite benefits.
The sea lice treatment welfare dilemma illustrates how animal welfare in aquaculture involves trade-offs between different welfare harms. Severe lice infestation causes chronic skin irritation, immune suppression, and susceptibility to secondary disease — all welfare harms. But the treatments used to control lice carry their own welfare costs: hydrogen peroxide at treatment concentrations causes respiratory distress; mechanical delicers cause physical trauma and mortality; warm water treatment causes thermal shock. Cleaner fish suffer arguably the worst welfare outcomes — wrasse and lumpfish introduced to net pens experience predation by salmon, starvation, and high mortality. The challenge of sea lice management — developing approaches that minimize both lice impacts and treatment impacts on millions of individual salmon — is a genuine welfare optimization problem.