Sea lice infestations are one of the most significant welfare challenges in farmed Atlantic salmon, causing skin damage, stress, and mortality. Management involves a difficult balance between treatment efficacy, fish welfare, and environmental impact.
Sea lice infestations cause significant suffering at enormous scale — billions of farmed salmon experience lice exposure annually. The skin lesions caused by feeding lice are painful, compromise immune function, and in severe infestations expose muscle tissue. Treatment procedures cause additional welfare impacts: chemical bath treatments cause acute stress; mechanical treatments (laser systems, warm water baths) cause thermal or physical stress. The wrasse cleaner fish used as biological control are themselves kept in poor welfare conditions within salmon cages. Environmental pressure to reduce chemical treatments conflicts with welfare pressure to control infestations. Integrated pest management combining biological, physical, and chemical tools represents the current best practice, with ongoing research into sea lice vaccines.