Sea lice infestation in farmed salmon causes significant welfare harm through tissue damage and chronic stress, and control methods including chemical treatments, cleaner fish, and mechanical removal each carry their own welfare implications.
Sea lice management in salmon farming presents a complex, compounding welfare problem. The lice themselves cause genuine harm through tissue destruction and osmotic stress. The treatments used to remove them — chemical baths, mechanical removal, thermal treatments — also cause acute stress and sometimes injury. The cleaner fish used as a biological control measure — wrasse and lumpfish — are themselves sentient fish whose welfare is poorly served by standard handling and husbandry in salmon cages. This layered welfare problem is intimately linked to the fundamental issue of high stocking density: lice spread rapidly in crowded pens, making control necessary but difficult. Fully enclosed recirculating aquaculture systems eliminate wild lice exposure entirely and represent the welfare-consistent direction for the industry, despite higher capital costs.