Recirculating aquaculture system

A land-based aquaculture system that treats and reuses most of its culture water, allowing fish or other aquatic organisms to be raised with limited water exchange.

Mechanical filtration: A separation process that removes suspended particles from a fluid using physical barriers or forces. It captures uneaten feed and feces before their breakdown adds dissolved waste to the loop.
Aquaculture: The farming of aquatic organisms, including fish, shellfish, and aquatic plants. Recirculating systems are one way to control the water environment in aquatic farming.
Atlantic salmon: A large migratory salmonid native to the North Atlantic, widely raised in aquaculture. Land-based salmon facilities use recirculation to grow fish through some or all production stages.
Flow-through aquaculture: Aquaculture that continuously supplies fresh water to culture units and discharges used water. Unlike recirculation, it relies on substantial water exchange rather than intensive treatment and reuse.
Biofilter: A treatment unit where microbial communities transform dissolved contaminants in water. Its microbes oxidize toxic ammonia excreted by fish into less harmful nitrate.
Ammonia toxicity in fish: Harmful effects on fish caused by exposure to ammonia in water. Excreted ammonia makes effective treatment essential, especially when water is reused.
Tilapia: A group of warm-water freshwater cichlid fishes widely farmed for food. Their tolerance of crowded, controlled conditions makes tilapia common in recirculating facilities.
Cage aquaculture: Fish farming in net enclosures placed in natural water bodies. Cages use surrounding waters directly, whereas recirculating systems isolate stock in land-based tanks.
Nitrification: The microbial oxidation of ammonia to nitrite and then nitrate. This biological process is the central route for controlling ammonia in a recirculating system.
Dissolved oxygen: Molecular oxygen dissolved in water and available to aquatic organisms and aerobic microbes. Fish and nitrifying bacteria both depend on oxygen supplied to the circulating water.

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