Recirculating aquaculture systems (RAS) are a fish production technology system where water exchange is limited often due to the high amount of fish in the system. The use of biofiltration is required for the toxic ammonia reduction. Environmental control is often used to maintain clean water and provide a suitable living environment for fish. The main benefit of RAS is the ability to reduce the need for fresh, clean water while still maintaining a healthy environment for fish. To be operated economically commercial RAS must have high fish stocking densities.
A well setup RAS system maintains: Biofiltration, Solid removal, Oxygenation, pH control, Temperature control, Biosecurity.
When a RAS system is combined with plants it's called an aquaponics system.