Sea lice treatments in salmon farming — thermal, mechanical, and chemical — all impose welfare costs. Understanding these costs is essential to selecting the least harmful management approaches.
Sea lice treatment creates a welfare double-bind: lice cause chronic suffering, and treatments to control them cause acute suffering. Every approach — thermal, mechanical, chemical, biological — imposes costs on the fish being treated. The welfare question is which approach minimises cumulative suffering across the grow-out period. Research suggests that the combination of chronic lice burden plus frequent aggressive treatment causes more welfare harm than either alone. Prevention-focused approaches — RAS systems, single-bay fallowing, selective breeding for lice resistance — aim to reduce treatment frequency by reducing lice establishment. These are welfare improvements, but their adoption is limited by cost and industry inertia.