Sea lice infestations are endemic in salmon aquaculture, causing painful tissue damage, immune suppression, and mortality in farmed fish while threatening wild salmon that encounter infected farms.
Sea lice cause genuine suffering in infested salmon. The parasites' feeding erodes skin and mucus coat - the salmon's primary barrier against disease and osmotic stress. The resulting lesions are open wounds that become infected. Thermal delousing treatments - immersing salmon briefly in warm water to kill lice - cause acute thermal stress and can cause injury if temperatures are not precisely controlled. Biological control using wrasse fish to clean lice from salmon creates welfare concerns for the wrasse, which experience high mortality in salmon farm environments. The endemic nature of lice in open-net salmon farming means that for billions of individual salmon, infestation and associated suffering are routine aspects of their short lives.