Farmed Atlantic Salmon in RAS: Recirculating Aquaculture Welfare

Recirculating aquaculture systems represent a growing technology for salmon farming that offers both welfare improvements and novel challenges compared to open-net pen farming.

Key Facts

Recirculating aquaculture systems (RAS) filter and recycle up to 99% of water, enabling inland salmon farming.
RAS eliminates sea lice infestations that affect open-net pen salmon, a significant welfare benefit.
Water quality parameters in RAS can be precisely controlled, avoiding the temperature and oxygen fluctuations of sea pens.
However, RAS systems can accumulate CO2 and ammonia if filtration fails, causing acute welfare crises.
Gas supersaturation in RAS has caused gas bubble disease in some facilities, damaging fish gills and eyes.
Stocking densities in RAS vary widely; high densities remain a welfare concern as in net pen farming.
Lighting and feeding regimes can be precisely optimised in RAS for fish welfare and growth.
RAS salmon farming is energy-intensive and the welfare benefits must be weighed against environmental costs.

Welfare Considerations

RAS salmon farming presents a mixed welfare picture. The elimination of sea lice — which in net pens cause chronic skin irritation, fin erosion, and anaemia — is a substantial welfare improvement. Precise environmental control enables optimal temperature and oxygen levels year-round. However, RAS creates new failure modes: sudden water quality crashes can affect thousands of fish simultaneously before detection. Gas bubble disease from supersaturation causes painful tissue damage. The psychological welfare implications of indoor tank environments versus sea pens are not well understood. Welfare monitoring in RAS requires investment in real-time sensor technology and trained staff capable of recognising subtle behavioural indicators of distress across large fish populations.

What You Can Do

Support certification schemes that set welfare standards for both net pen and RAS salmon farming.
Ask retailers about the farming method and welfare standards of their salmon products.
Advocate for real-time water quality monitoring standards in RAS facilities.
Support research into fish welfare assessment tools applicable to RAS environments.
Consider salmon consumption frequency and source as part of an informed sustainable seafood choice.
Engage with aquaculture certification bodies (ASC) to strengthen welfare requirements.