Farmed Salmon RAS Welfare: Recirculating Aquaculture Systems

Recirculating aquaculture systems (RAS) for Atlantic salmon are promoted as environmentally superior to sea cage farming, but their welfare implications are complex. Controlled environments can improve or worsen welfare depending on management quality.

Key Facts

RAS facilities recycle 95-99% of water, eliminating sea lice and reducing environmental discharge
Atlantic salmon in RAS are exposed to stable temperature and oxygen levels that can be optimized for growth
However, high stocking densities in RAS — sometimes exceeding 80 kg/m² — cause chronic crowding stress
RAS salmon cannot perform natural migratory behavior or experience natural light cycles without active management
Cataracts are a significant welfare problem in RAS salmon, linked to inadequate diet and UV light exposure
Amoebic gill disease, a major welfare concern in sea cage systems, is absent in well-managed RAS
Cardiovascular abnormalities are common in fast-growing RAS salmon due to selection for rapid growth
Norwegian and Scottish regulators are developing RAS-specific welfare standards separate from sea cage frameworks

Welfare Considerations

RAS welfare outcomes are highly system-dependent. The elimination of sea lice — a major welfare benefit — is offset by the welfare risks of extreme stocking densities and unnatural light/temperature cycles. Crowding causes fin damage, aggression, and chronic stress measurable through cortisol levels and immune suppression. Cataract prevalence of 30-80% in some RAS facilities indicates nutritional or light management failures causing visual impairment. The positive welfare potential of RAS — controlled environment, disease management, no sea lice — can only be realized through management practices that prioritize fish welfare alongside efficiency. RAS welfare science is emerging rapidly, with opportunities to design systems around fish behavioral and physiological needs from the outset rather than retrofitting welfare into existing designs.

What You Can Do

Support aquaculture certification schemes that include RAS-specific welfare standards
Ask salmon retailers about stocking density and welfare monitoring in their RAS supply chains
Advocate for regulators to develop evidence-based RAS welfare standards
Reduce salmon consumption and shift toward higher-welfare certified products when consuming fish
Support research into RAS design optimization that improves welfare without sacrificing efficiency
Learn about the trade-offs between different salmon farming systems to make informed choices