Sea lice infestations are one of the major welfare challenges in farmed salmon, and treatments have their own welfare implications.
Sea lice cause chronic pain through tissue damage at attachment sites. Heavy infestations cause open lesions on the head and back that allow secondary bacterial and fungal infections. The treatments used to control lice each have their own welfare implications - hydrogen peroxide causes oxygen depletion during treatment, thermal treatments cause stress, and handling during mechanical removal causes additional stress. The welfare of cleaner fish used as biological controls often receives inadequate attention - wrasse and lumpfish suffer high mortality rates in salmon farms. A welfare-optimal approach minimizes both lice burden and treatment stress, but this is rarely achieved in practice.