Sea lice are a major parasite challenge in Atlantic salmon farming, and the treatments used to control them raise significant welfare concerns for both target and non-target species.
Sea lice treatment welfare affects both salmon and the treatments themselves. Bath treatments using chemicals require salmon to be crowded into treatment wells with chemical-containing water — a stressful procedure causing fin damage and mortality in poorly managed operations. Thermolicer treatment uses 34-degree water to kill lice, causing thermal shock that results in mortality rates of 0.5-2% per treatment. Laser treatment is non-chemical but causes fish to be processed through equipment multiple times. Snorkel barriers and deep feeding systems that keep salmon below surface lice reduce treatment need but don't eliminate it. Cleaner wrasse used as biological control suffer high mortality themselves in salmon farm conditions — the welfare cost of wrasse may approach or exceed the welfare benefit to salmon.