Reuse technology in the Northeast is most commonly used to culture trout in raceways linked in series. Laws that regulate effluents of flow through systems also apply to discharges from reuse systems. Fish are normally raised in tanks where they live, eat, respire, and excrete. Particulate wastes are removed by a primary filter. The water is then returned to the fish holding unit.
Water is added to replace that lost by evaporation and discharged to remove settled solids.
These systems require continuous aeration or oxygenation of both the fish culture tanks and biological filter to function properly. Water quality must be monitored closely and emergency back-up systems are essential. Recirculating systems are potentially appropriate when water quality and quantity are insufficient, for example if water must be cooled or warmed, or if discharge standards are strict . While the culture of fish in recirculating systems is biologically possible, the economics must be very carefully studied. These systems require high value species and experienced operators for commercial success.