Sea lice infestations are a major welfare challenge in farmed salmon causing painful lesions. Management approaches vary in their welfare and environmental impacts.
Sea lice represent a significant and persistent welfare problem in open-net salmon farming. Heavy lice burdens cause visible lesions particularly around the head and dorsal fin that are painful and create entry points for secondary infections. The inflammation and immune activation of chronic infestation constitutes ongoing welfare compromise. Treatment methods themselves have welfare implications: hydrogen peroxide baths cause temporary stress and potential mortality in sensitive individuals, while mechanical de-lousing methods can cause physical injury. Cleaner fish including wrasse and lumpfish used as biological control present their own welfare concerns as non-target species in an alien environment. Closed containment systems that prevent lice transmission offer the most comprehensive welfare and environmental solution.