Sea lice infestations on farmed Atlantic salmon cause chronic pain and tissue damage, representing one of the most significant welfare challenges in aquaculture.
Sea lice cause significant suffering to farmed salmon through direct tissue damage from feeding activity, which produces open sores and exposes underlying muscle and skull in severe cases. Affected fish show avoidance behaviors, reduced feeding, and impaired osmoregulation. Treatment methods including hydrogen peroxide baths and mechanical louse removal are themselves acutely stressful. The precautionary principle and growing evidence for fish sentience mean this welfare problem demands urgent industry-wide attention beyond economic motivations.