Sea lice are ectoparasites that cause significant welfare suffering in farmed Atlantic salmon and pose a serious conservation threat to wild salmon passing through farming areas.
Sea lice represent one of the most significant welfare challenges in Atlantic salmon farming, causing chronic pain through skin lesion progression and acute stress from treatment procedures. The welfare of farmed salmon and wild salmon are interconnected through the louse spillover effect: high louse burdens on farms elevate ambient louse pressure for wild fish in shared waters. Treatment itself creates welfare trade-offs — chemical bath treatments cause handling stress, oxygen depletion, and occasionally direct mortality. Thermal treatments (heated water) cause acute stress and scale loss. Laser systems are less stressful but expensive. Reducing louse burden through integrated pest management — including genetic selection for resistance, cleaner fish, and biological controls — is the long-term welfare solution, but requires significant investment and sustained commitment.