RAS design basics: from output to equipment

1. Target output to standing stock

Annual output, harvest size and growth rate set how many fish are in the tanks at any time. This is the standing stock, and the tanks must hold it at a density the species tolerates.

2. Standing stock to tank volume

Standing stock divided by the planned stocking density gives the culture volume. Splitting it into tanks depends on the species, the building and how you plan to grade and harvest.

3. Fish to feed

Feed rate depends on species, size and temperature. The peak daily feed is the most important number in the design: it sets the load on every treatment stage. Extension guides describe the same order: the harvest sets the standing biomass, the biomass and feeding rate set the peak daily feed, and the feed sizes every treatment stage (SRAC).

4. Feed to treatment load

• Ammonia from feed protein sizes the biofilter.
• Solids from faeces and uneaten feed size the mechanical filtration.
• Oxygen demand after feeding sizes the oxygen supply.
• CO₂ from respiration sizes degassing.

A common rule of thumb is about 350 g of oxygen per kg of feed for the fish (Novair). The biofilter and organic matter use more on top.

5. Load to flow

The flow through the tanks must bring enough oxygen and carry waste out fast. Flow also sets the size of the drum filter, pumps, pipework and UV.

6. Flow and load to equipment

Each stage is then sized on the flow and load it carries, at the peak, with standby units where a failure would harm the fish. See how to select RAS equipment.

7. Check the balance

The last step is to check that every stage agrees: the same flow, the same feed load and enough margin at the peak. This flow balance is what we send with every first layout.

Fit the site

Building size, climate, water source and power then shape the layout, heating or cooling, and materials. Send species, target output and site size and we return a first layout in 3 days, free.