Recirculation aquaculture systems (RAS) represent a new and unique way to farm fish. Instead of the traditional method of growing fish outdoors in open ponds and raceways,this system rears fish at high densities, in indoor tanks with a "controlled" environment.

Recirculating systems filter and clean the water for recycling back through fish culture tanks.New water is added to the tanks only to make up for splash out and evaporation and for that used to flush out waste materials.

Fish grown in RAS must be supplied with all the conditions necessary to remain healthy and grow. They need a continuous supply of clean water at a temperature and dissolved oxygen content that is optimum for growth. A filtering (biofilter) system is necessary to purify the water and remove or detoxify harmful waste products and uneaten feed. The fish must be fed a nutritionally-complete feed on a daily basis to encourage fast growth and high survival.