Recirculating Aqua Culture

Recirculating Aqua Culture | How does work RAS Fish Farming

What is a Recirculating Aquaculture System or RAS?

In a re-circulating aquaculture system, the water used for fish farming is treated and continuously reused. The re-circulating aquaculture system is an almost completely closed circuit. The wastes or solid wastes produced in the fish pond, ammonium, and CO2 are removed during the operation of the RAS system or converted into non-toxic products. The treated water is then returned to the fish tanks. By circulating the water in the fish tank in this way, the water and energy requirements can be kept to a minimum. However, it is essential to add water in a minimal way through re-circulating aquaculture. The non-rotting waste or celery should be removed and the evaporated water should be re-poured as much as possible. However, our re-circulating systems can reuse 90% or more of the purified water. A lot of systems are essential in a well-functioning RAS unit. A detailed description of RAS technology is essential.

Benefits or advantages of a Recirculating Aquaculture System (RAS).

  • Low water use. The water used for fish farming is re-treated and only a small amount of water has to be added.
  • Electricity is essential 24 hours a day. Although the use of electricity is a bit higher than other types of fish farming, fish farming can be done profitably under the RAS system if the special tariff given by the Electricity Board for fish farming is utilized.
  • Efficient Land Use – Another feature is that it can grow more fish in less space. Natural ponds can harvest up to 5 kg of fish per cubic meter of water while a re-circulating aquaculture system can harvest up to 40 kg.
  • Another feature of such a close unit is that it can optimize the optimal feeding or feeding of the fish.
  • Fish can also be easily sorted and harvested in units like this.
  • Complete disease control. Diseases of fish are a common problem in aquaculture. Diseases found in this way can be easily treated and treated in closed units like this
  • Another advantage of this is that it is possible to grow fish using the RAS aquaculture method in any climatic country or region. In countries with moderate frosts, fish are grown in bulk indoors using the RAS system


Basic principles of a re-circulating aquaculture system and the components required for it.

  1. Fish tank
  2. Mechanical filter
  3. Biological filter
  4. Water pump for rotating water
  5. Aerators or blowers are needed to supply oxygen.
  6. These are important, but if they are large units, UV light, oxygen feeders, auto feeders, etc. can be used.

Onyx Aquaponics Farm in Kerala

Important factors of Recirculating Aquaculture System (RAS).

Mechanical filter

In a RAS system, the system uses a mechanical filter to remove suspended solids or solid waste from the water. Removal of such solids or fish waste and residues from fish feed is essential for maintaining water quality. Bio sponges and nets are used in small units to prepare the mechanical filter. But in larger units the drum filters are used as the mechanical filter. The drum filter is best known for its functionality and slurry removal. But it is a lot more expensive than mechanical fitters made with bio-sponge net in standard units.

Filter Unit of Aquaponics fish farmingBLACK SPONGE 20"*20"*2"

Recently a friend used 3 barrels of 200 litters to prepare a mechanical filter for a RAS system that holds 50,000 litters of water. Six bio-sponges, each two inches thick, were used in each barrel. It is said that this system is capable of removing solid waste in a good way.

Sedimentation filter.

If required, the water flowing from the fish tank to the mechanical filter can be drained through the sedimentation tank. Insoluble solids in this tank can be trapped at the bottom of the tank by gravity and can be prevented from reaching the mechanical filter by means of a drain out system.

Biological Filter

The biological filter, or bio filter, is an important component of the filtration component of the re-circulating aquaculture system (RAS). The bio-filter contains nitrifying bacteria, or bio-filter, which is the first unit in which the nitrification process takes place. Ammonia is formed from fish waste, and the rest of the fish’s feed is deposited in the pond. This waste product is toxic to fish and can cause stress to fish. This leads to reduced growth rate and higher rate of fish death. However, the bacteria that naturally occur in the biological filter oxidize the ammonia and use it to grow and convert it to nitrite (NO2-). This is an aerobic process that requires oxygen. Bacteria that convert ammonia to nitrite are known as Nitrosomonas. Like ammonia, nitrite produced by Nitrosomonas bacteria is harmful to fish. Nitrite greater than 5 mg / litter can lead to fish death.

However, bacteria known as Nitrobacter oxidize the nitrite (NO2-) produced by Nitrosomonas and convert it to nitrate (NO3). Oxygen is also essential for this function. Nitrate is the end product of the conversion of Ammonia and Nitrite, and usually 200 mg / Litter in the RAS system is not harmful to fish. This process takes place in a bio-filter in a re-circulating aquaculture system (RAS).

The most commonly used media in a bio filter are bio balls and MBBR. These media prepare the surface for bacteria to live. As these bacteria give rise to overgrowth, more and more build up inside the bio filter.

K5 MBBR Filter MediaBio-Filter Media MBBR (1 L) for Aquarium Fish TanksBio-Balls for Fish Tank Filtration

The mechanical filter as well as the bio filter is the only 2 indispensable units of a re-circulating aquaculture system. But in addition to this, Other equipment such as UV-C light, oxygenation equipment or ozone oxygenator, and feeders required for automatic feeding of fish can also be installed.

The importance of UV-C Light in a RAS system has to be explained through a video itself. Let’s do another video about this. This video tries to explain the function of a re-circulating aquaculture system and its important components. You can leave your comments and doubts about the video below. If you like this video, don’t forget to share it with others and subscribe to the channel.

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