The methods used to treat sea lice on farmed salmon — including thermal, mechanical, and chemical approaches — carry significant welfare costs that are increasingly scrutinized by welfare scientists.
Sea lice treatment welfare creates a difficult compounding problem: the lice themselves cause suffering, and the treatments used to remove them also cause suffering, often repeatedly across a single production cycle. Each treatment event involves crowding, handling, acute thermal or mechanical stress, and recovery periods during which fish show suppressed feeding and elevated stress indicators. The cumulative welfare cost across multiple treatments can be substantial. The welfare case for prevention — through site selection, reduced stocking densities, improved monitoring, and cleaner fish integration — is compelling precisely because it reduces the frequency of these acute treatment events. Industry incentives to minimize treatment frequency (due to costs and fish mortality) partially align with welfare goals, but only if prevention is effectively achieved.