Recirculating Aquaculture Systems and Salmon Welfare

Recirculating aquaculture systems (RAS) promise environmental benefits over sea cage salmon farming, but their welfare implications for fish are complex and require careful evaluation.

Key Facts

RAS facilities recycle up to 99% of their water, dramatically reducing environmental footprint compared to sea cages.
Land-based RAS eliminates sea lice and escape risks but creates novel welfare challenges from artificial conditions.
Water quality parameters in RAS — CO2, ammonia, dissolved oxygen — must be precisely managed to avoid chronic stress.
High-intensity artificial lighting and high fish densities in RAS raise welfare concerns not present in sea cage systems.
Several major RAS salmon facilities have experienced catastrophic mortality events from system failures.
RAS salmon cannot exhibit natural migratory behaviour or experience the marine environment at any life stage.

Welfare Considerations

RAS salmon welfare presents a nuanced picture that requires moving beyond simple environmental vs. conventional comparisons. While RAS eliminates the serious welfare challenges of sea lice treatment and escape-related ecological harm, it introduces distinct stressors. Constant artificial lighting without appropriate dark periods disrupts circadian rhythms and increases cortisol. Very high stocking densities — sometimes higher than sea cages — increase aggression and fin damage. Elevated dissolved CO2, a common challenge in RAS water management, causes physiological stress and potential acidosis. System failure events — power cuts, pump failures, oxygen drops — can cause mass mortality within hours. Positive welfare indicators in RAS salmon including voluntary swimming patterns, fin condition, and feeding motivation must be monitored alongside mortality rates. The highest-welfare RAS systems incorporate photoperiod management, appropriate density targets, and robust welfare monitoring protocols alongside their environmental management plans.

What You Can Do

Ask salmon producers whether RAS or sea cage systems are used, and what welfare monitoring protocols they employ.
Support research into RAS welfare optimisation, particularly around photoperiod management and density standards.
Advocate for welfare assessment requirements in planning approvals for new large-scale RAS facilities.
Choose salmon from producers with transparent welfare reporting, regardless of production system.
Reduce overall salmon consumption and consider plant-based alternatives to reduce demand on intensive systems.