Farmed Salmon Open-Net Pen Welfare: Sea Lice

Sea lice infestation is the most significant welfare problem in Atlantic salmon farming in open-net pen systems, causing tissue damage, pain, and immune compromise.

Key Facts

Lepeophtheirus salmonis and Caligus species are the primary sea lice species affecting farmed Atlantic salmon
Lice attach to the skin and gill surfaces, feeding on mucus, skin, and blood and causing progressive lesions
Infested fish show reduced growth, increased stress responses, and secondary bacterial infections
Delousing treatments include chemical bath treatments, hydrogen peroxide, and biological control using cleaner fish
The welfare of cleaner fish used to control sea lice — particularly lumpfish — is itself a growing concern

Welfare Considerations

Sea lice infestation causes chronic suffering through skin and gill damage that impairs osmoregulation, causes physical pain from tissue destruction, and creates entry points for secondary infection. Heavy infestations produce visible lesions on the head and back. Delousing treatments — while necessary to control lice — cause additional acute welfare stress through handling, bath treatment exposure, and mechanical systems. The welfare implications cascade: lice cause suffering, treatment causes acute stress, and resistance to treatments is increasing due to overuse. Recirculating aquaculture systems that physically exclude lice represent a welfare improvement by eliminating the infestation problem entirely.

What You Can Do

Support investment in land-based recirculating aquaculture systems that avoid sea lice infestation entirely
Choose salmon from farms with demonstrated low sea lice levels and welfare-aware treatment approaches
Advocate for welfare standards for cleaner fish used in biological sea lice control
Support research into non-chemical sea lice control methods with lower welfare side effects