Salmon Aquaculture: Lice Treatment Welfare

Sea lice are a major parasite problem in salmon aquaculture. The treatments used to control them have significant welfare implications for farmed and wild salmon populations.

Key Facts

Sea lice (Lepeophtheirus salmonis and Caligus spp.) are ectoparasites that graze on salmon skin and mucus
Lice infestations cause wounds, osmotic stress, reduced feeding, and increased susceptibility to disease
Chemical treatments including hydrogen peroxide and azamethiphos baths are commonly used
Mechanical treatments including warm water and laser systems are alternatives with different welfare profiles
Cleaner fish (wrasse and lumpfish) are used as biological control agents, raising separate welfare concerns
Wild salmon populations are affected by lice spillover from farm sites located on migration routes

Welfare Considerations

Lice treatment is one of the most acutely stressful husbandry procedures in salmon aquaculture. Bath treatments involve crowding fish into treatment pontoons, exposure to chemical solutions, and often hypoxic conditions during and after treatment. Mortality events during lice treatment are a documented welfare and production problem. Mechanical thermal delousing using warm water is effective but causes physical stress including scale loss and surface injuries. The welfare of cleaner fish used in biological control is increasingly recognised as a concern — wrasse in particular have complex social and habitat needs that are not met in intensive farm settings.

What You Can Do

Choose salmon certified under RSPCA Assured or ASC schemes that include lice monitoring standards
Ask salmon retailers about their suppliers' lice treatment methods and mortality event records
Support research into next-generation lice control methods that minimise treatment stress
Advocate for salmon farm siting regulations that protect wild salmon migration routes from lice spillover
Consider reducing farmed salmon consumption pending sector-wide welfare improvements