Sea lice infestations are among the most serious welfare problems in Atlantic salmon farming, causing chronic pain, secondary disease and high mortality rates.
Sea lice infestations in farmed salmon cause chronic pain and distress that builds over weeks. Early infestations cause irritation and altered swimming behaviour; severe infestations produce grotesque tissue damage including exposure of the skull bone and penetration into brain tissue. Treatments — hydrogen peroxide baths, medicinal chemicals, biological cleaner wrasse — vary in effectiveness and carry their own welfare costs. The ecological spillover to wild salmonids creates a welfare harm that extends beyond the farm fence. Land-based closed containment eliminates the problem but requires substantial capital investment.