Sea lice are parasitic copepods that cause serious welfare problems for farmed Atlantic salmon, with high infestation burdens causing pain, skin damage, and secondary infections that affect millions of fish annually.
Sea lice cause genuine suffering in farmed salmon. Research supports salmon sentience and capacity for pain, making the tissue damage from heavy infestations a significant welfare concern. Mechanical delousing treatments including warm water baths and pressure washing also cause acute stress and can be fatal when fish are in poor condition. The use of cleaner fish creates a cascade of welfare problems as wrasse and lumpfish are often sourced from poor conditions and have high mortality rates on salmon farms. Addressing sea lice through improved net pen design and lower stocking densities is more effective for welfare but less economically attractive to producers.