Sea lice infestations are a persistent welfare crisis in Atlantic salmon aquaculture, causing painful skin damage, stress, and death while simultaneously threatening wild salmon populations.
Sea lice represent one of the most significant welfare problems in commercial salmon farming. The tissue damage caused by heavy infestations is equivalent to severe chemical burns across a large proportion of the body surface. Secondary bacterial and fungal infections enter through lice-damaged skin and cause additional suffering. Fish experiencing heavy lice burdens show altered behavior, reduced feeding, and increased stress hormone levels. Treatment itself causes welfare stress — chemical bath treatments cause disorientation and physical stress, while mechanical delousing devices cause physical trauma. The welfare of cleaner fish used in biological control is also increasingly recognized as requiring attention, as wrasse and lumpfish used in Scottish farms often have inadequate conditions.