Sea lice are a major welfare and economic problem in salmon farming. The treatments used to control them carry their own welfare costs, creating difficult trade-offs in aquaculture management.
Sea lice management presents a genuine welfare dilemma: untreated infestations cause chronic suffering through tissue damage, secondary infection, and physiological stress, while available treatments themselves cause acute pain and injury. Chemical bath treatments expose fish to compounds that can cause gill damage, chemical burns, and acute physiological stress. Mechanical treatments cause physical injury through water pressure or temperature shock. The development of less invasive treatment technologies including laser delousing represents genuine progress but is not yet universally deployed. Wrasse used as cleaner fish to eat lice from salmon face their own welfare challenges including mortality during capture and transport, and inadequate conditions in salmon cages. Reducing lice burdens through improved farm siting, reduced stocking density, and earlier intervention reduces the need for high-frequency treatments.