RAS Design for Atlantic Salmon: Stages, Water Treatment and Key Choices

A salmon RAS follows the same principles as any recirculating system, but cold water, a long cycle and a sensitive species raise the stakes on every design decision. These are the choices that shape the layout and the budget.

Stages and cohorts

Most designs separate the fish into stages — hatchery or smolt, post-smolt and grow-out — each with its own tank sizes and water treatment loop. Running several cohorts in parallel keeps harvests regular but needs more tank groups. Separate loops also limit how far a disease outbreak can spread.

Size from feed load, not tank volume

Peak daily feed drives oxygen demand, waste production and ammonia load, and so the size of drum filters, biofilters, oxygen systems and pumps. The method is in sizing a RAS from feed load to oxygen demand, and you can check numbers in the oxygen demand calculator.

Cold-water biofiltration

Nitrifying bacteria work more slowly in cold water, so salmon systems usually need more biofilter capacity than warm-water farms of the same feed load. Start-up time for the biofilter also needs to be planned before the first fish arrive.

CO2 removal and gas balance

At high stocking densities, carbon dioxide builds up quickly and harms fish health and growth. Degassing towers or strippers, adequate airflow in the building and good monitoring are central to a salmon design, not optional extras.

Temperature control

Depending on climate and water source, chillers, heat pumps or heat exchangers keep water in the right range. The building's insulation and air handling affect both energy cost and condensation.

Disinfection and biosecurity

UV or ozone, controlled water intake, foot and equipment hygiene and separate zones for each stage reduce disease risk. The principles are covered in biosecurity zoning and HACCP.

Purging before harvest

Many land-based salmon farms move fish to clean-water purging tanks before harvest to remove off-flavour compounds. Plan the tanks, water supply and time this needs into the layout from the start.

Redundancy and backup

Pumps, oxygen supply, blowers and power need backup sized to keep fish alive through a failure. In salmon RAS, where biomass is high and cycles long, a single failure can cost a whole cohort. See RAS design fundamentals before equipment and the costs that follow in RAS salmon farm costs.

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