Farmed Salmon Welfare in Recirculating Aquaculture Systems

Recirculating aquaculture systems eliminate sea lice and reduce environmental impact compared to open net pens, but create new welfare challenges for salmon including elevated CO2 levels and density-related stress.

Key Facts

Recirculating aquaculture systems (RAS) filter and recycle water in enclosed tanks, preventing disease exchange with wild fish
RAS facilities can be located inland, near markets, and without access to ocean areas, decoupling salmon farming from coastal ecosystems
Despite eliminating sea lice, RAS creates new welfare challenges including elevated dissolved CO2 levels that cause chronic respiratory stress
High CO2 in recirculated water impairs salmon sensory function, including their ability to detect predators and orient in their environment
Stocking densities in RAS can be very high — up to 80-100 kg per cubic metre — causing chronic stress and aggression
Cataracts occur at high rates in RAS salmon due to nutritional factors and water quality differences from natural conditions
Snout damage from collision with tank walls and equipment is a common welfare indicator in early RAS systems
Advanced RAS with careful oxygen management, moderate stocking, and appropriate flow rates show better welfare outcomes
Norway and Scotland are investing heavily in RAS as an alternative to coastal net pens for both welfare and environmental reasons
Life Cycle Assessment studies show RAS has higher energy use but lower total ecological impact than sea-based net pens

Welfare Considerations

RAS represents an important step toward more environmentally sustainable salmon farming, but the technology transition does not automatically deliver better fish welfare. Some early RAS operations produced fish in worse welfare conditions than net pens due to poor water quality management. As the technology matures and welfare standards develop, the potential exists for RAS to combine environmental sustainability with meaningful welfare improvement — but this requires commitment from producers and certification bodies to embed welfare monitoring from the outset.

What You Can Do

Choose salmon from RAS operations certified under welfare standards that include CO2 monitoring and stocking density limits
Ask retailers about the production system and welfare certification of farmed salmon they stock
Support research into optimal RAS water quality parameters for salmon welfare outcomes
Advocate for welfare standards that specifically address RAS-unique challenges including CO2 and cataract monitoring
Reduce farmed salmon consumption or choose certified alternatives while welfare standards develop
Support industry transition to RAS combined with genuine welfare monitoring requirements