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Recirculation Aquaculture Systems (RAS)

Eel Recirculation System

Recirculation Aquaculture Systems (RAS) basically consist of culture tanks for aquatic organisms and a water treatment system that is designed to maintain optimum conditions for the culture species. This allows the water to be recycled continuously.

Fish, crustaceans and shellfish consume feed and oxygen and produce carbondioxide, urea, ammonia and feces. The technical components of the RAS are designed to remove the waste products and supply oxygen. At the same time the water treatment system must maintain optimum culture conditions with respect to for example pH; salinity and alkalinity and must minimize stress and concentrations of parasites and pathogens.

Main components in RAS include settlers, drumfilters and foam fractionators for solid removal; trickling biofilters or submerged moving bed biofilters for removal of ammonia and carbondioxide; heaters and chillers for temperature control; UV lamps or ozone for disinfection and oxygen reactors for oxygen addition. For emergency situations the systems are equipped with some form of in-tank emergency oxygenation, alarm systems and power generators. Other important components include feeding- and grading systems.

Normally RAS are housed in an insulated building, to enable better control of the farming environment, especially temperature.

RAS allow the efficient production of aquatic species with minimum quantities of water. By maintaining the optimum culture temperature the cold-blooded species can grow at maximum speed, often 2-3 faster than in the natural environment. Fast growth is normally accompanied with a high feed utilization efficiency, minimizing the feed cost.

Although RAS were being developed only 30 years ago they have now reached a point that in many cases this type of aquatic production systems can compete with pond- and cage culture.

Although the total amount of fish produced in these systems is small compared to other culture methods RAS are successfully used for production of, for example Eel (Anguilla sp.); Catfish (Clarias and Hetrobranchus sp.); Tilapia (Oreochromis sp.); Salmon (Salmo sp.); Trout (Oncorhyngus sp.); Yellowtail (Seriola sp.) and ornamental fish.



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