RAS Fish Farming in India; Techniques; Setup Guide

RAS fish farming in India,  Setup, Techniques

Let us get into the details of RAS Fish Farming in India, RAS setup, cost, and Techniques involved in RAS fish farming in India.

Introduction to RAS:

What is RAS?, Instead of the traditional method of growing fish outdoors in Open Ocean, ponds or raceways, Recirculating aquaculture systems (RAS) rears fish in a closed containment system with a “controlled” environment. Recirculating systems filter the water for recycling back through to the fish, recovering waste products that can give nutrients for vegetable production in an Aquaponics system. The steps in RAS include solids removal, ammonia removal, Co2 removal & oxygenation. RAS is used in home aquaria & for fish production where water exchange is limited & the use of biofiltration is necessary to reduce ammonia toxicity.

Fish grown in RAS must be supplied with all the conditions essential to remain healthy and grow. They need a continuous supply of clean water at a temperature & dissolved oxygen content that is optimized for growth. A filtering or biofilter system is necessary to purify the water & 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 & high survival. How does a recirculating aquaculture system work? RAS work by clean water from the fish tanks so it can be reused within the tank. This dramatically reduces the amount of water & space required to intensively produce seafood products.

RAS fish farming system setup:

The main system has a simple design which consists of fish tanks, mechanical filter, biofilter, oxygen enrichment unit & UV disinfector. Also need some more facilities such as pH regulator, heat exchange unit and denitrification unit, etc.

Location flexibility:

RAS is particularly useful in areas where land & water are expensive and not readily available. They require moderately small amounts of land and water. They are most suitable in northern areas where a cold or cool climate can slow fish growth in outdoor systems & prevent year-round production. The RAS system provides growers who are geographically disadvantaged because of a relatively short growing season or extremely dry conditions, profitable, year-round fish production system. They can be located close to large markets and thereby reduce hauling distances & transportation costs. RAS can use municipal water supplies & discharge waste into sanitary sewer systems. Nearly all species of food fish and sport fish that are normally reared in ponds, including catfish, trout, and striped bass can readily be grown in high densities when confined in tank systems.

RAS fish tank:

The tanks used in the RAS fish farming system can be of any size & shape. The RAS tank can be rectangular, circular, oval, etc. Mostly the circular tanks are chosen the RAS fish farming system because they are easier to clean & also facilitate easy water circulation when compared to rectangular tanks. The size of the tanks can vary from 500 gallons to 500k gallons depending on the existing facilities. The capacity of the tank depends on the factors like type of fish, stocking rate, water requirement & quality. The materials which are used for constructing the tanks can be wood, glass, rubber, metal, concrete or plastic.

Today, most of the modern tanks are being constructed with outlets that have optimal waste removal capacity & are fitted with suitable mesh screens. These outlets must also make removal of dead fish easy. Raceway tanks are used which is a blend of circular and rectangular shapes. These RAS tanks have a wall in the center for facilitating circulation. To know of the culture tank, the size of the culture tank depends on the quantity of water availability. This will finally lead to the choice of the fingerlings or the broodstock required depending on the scientific skills & the ability to maintain them by proper feeding, adequate oxygen supply, optimum pH control, and waste removal. Sump for the waste collection The presence of waste in the tank decreases the amount of dissolved oxygen content in water & increases the demand for oxygen. So a clarifier tank is used for collecting the excess waste at a slow rate. The shape of the sump must be of V shape so as to facilitate easy cleaning.

Water supply:

A good supply of water, adequate in both quantity & quality, is essential to a successful fish farming enterprise, RAS or otherwise. Groundwater obtained from deep wells or springs is the best supply of water for fish culture. It generally is free of pollutants & has relatively high hardness levels, which are beneficial under some circumstances. Municipal water supplies can be used after chlorine, fluoride, and other chemicals are removed.

Other sources of water, mainly surface waters of streams, rivers, ponds, and lakes, are not recommended for fish culture. Surface waters may have fish diseases, parasites, pesticides, and other pollutants that can kill or slow the growth of fish. Testing the quantity & quality of the available water supply is one of the first steps for a prospective fish farmer to take to ensure an adequate supply of high-quality water. For a flow of water and pumps, there should be a constant flow of water in Recirculating aquaculture fish farming system, and there must be a possibility to alter the speed, pressure & direction depending on the requirement. Commonly the movement of water is controlled through gravitation & before it is used in the system, the water is usually pumped to an elevation from where it begins to flow.

Normally the centrifugal pump is most commonly used in the RAS fish farming system. Usually, the pump is placed outside the tank & operates at high pressure. For removal of impurities, both suspended & settleable impurities are removed from the culture tanks after a series of tests done on the manage parameters like pH, temperature, and the nitrogenous wastes like ammonium wastes. If these parameters are found in the extreme & are not good for the survival of fish, then water is flushed out of the tanks through drains. The tank is refilled with a new volume of water & a little quantity of salt is added to the new water to activate or revive the behavior of the fish in the new water environment.

Recirculation components:

There are numerous designs for aquaculture systems utilizing biofiltration, ranging from an easy tank biofilter to high tech designs with computer controls. However, all systems have definite basic components. All these components may be separate pieces, or several may be integrated into a single unit.

All systems require a water supply, and tanks to rear fish in, a method of removing particulate wastes, the biofilters, a method to re-oxygenate the water & a method to remove water. In addition, there are numerous support facilities which must be considered, including, the building to house the facilities, the heating or cooling systems, food storage facilities, transport facilities, and back-up equipment. Solid removal in recirculation systems is one of the key problems in RAS is related to a load of suspended & in particular to very fine particles. The presence & accumulation of particulate wastes in RAS will negatively impact the water quality by affecting the performance efficiency of the water treatment units. High suspended solids load has several disadvantages:

  • Particulate matter consumes oxygen through biological degradation which will decrease the availability of oxygen for fish culture.
  • The breakdown of organic wastes will increase the Total Ammonia Nitrogen (TAN) concentration in the water moving nitrification. Small quantities of unionized ammonia can be toxic to epithelial tissues & disturb the elimination of protein metabolites across the gills.
  • Solids support the growth of heterotrophic bacteria which can outgrow & compete with nitrifies. The nitrification procedure is strongly inhibited by heterotrophic processes when high amounts of organic carbon are present.
  • Particles can potentially clog biofilters & reduce their efficiency
  • Excessive solid loads can cause plugging within aeration columns, screens, and spray nozzles orifices, which can ultimately result in system failure.

A RAS system comprises of a number of major components that are essential for the management of the system, these contain:

  • Site and components
  • System components

Site Components

The site components include equipment & structures that are not part of the recirculation system. a) Building

An isolated building or shed is necessary to protect the RAS from external climatic conditions. It will ensure that the environment in which the fish are cultured is controlled & maintained.

  1. b) Pump House

This houses the pump that will move water & air through the system. Its function is to give protection to the pump ensuring that it does not come into contact with the moisture formed from humidity that could potentially damage the pump.

  1. c) Three phases of electricity

Electricity is required to run lighting, filtration systems, heating, etc. Three phase power is preferable to single phase electricity due to the high energy consumption requirements from the system & the kind of total heat production.

  1. d) Emergency generator

This is necessary just in case, mains power is disconnected due to faults, overloading or maintenance. Fish can survive for very short periods without oxygen or infiltration.

  1. e) Bulk feed storage

A large quantity of food is necessary to feed large numbers of fish, storage facilities are required to protect food from vermin as well as mildew & mould caused by moisture.

  1. f) Purging

Fish will want to be purged to expel waste matter before they are sent to the markets.


Accumulated gases in the fish tank must be cleared by providing proper aeration. And this process is called stripping. Supplying air into the tanks can drive the gases away during turbulence. And a trickling filter system is often used for this method.

Mechanical filtration:

Mechanical filtration basically removes both settleables & suspended solid materials. Settleable solids are removed during the drains that are placed at the bottom in circular tanks. Circular flow patterns having agitation & this helps the solids to accumulate at the bottom and remove in the flow leaving the tank. Some solids are removed from the surface, while on slower flows on the other hand effect on accumulation at the bottom of the tank. Mechanical filters need regular back-flushing to prevent the accumulation of sludge.

Suspended solid materials obtained from not- eaten food is removed by the use of a screen filter (the drum filter). This is due to the following advantages over another system:

  • It could be adjusted to solids loading
  • It has a larger surface area than normal disk filters
  • It does not have the chance of collapsing under high loading rates of solids

Removal of solids is important to ensure that pipes & equipment components do not become clogged with waste materials. Decomposing waste matter left in the fish tank will consume available oxygen within the water column.

Foam fractionation:

Many of the fines suspended solids & dissolved organic solids that build up within intensive recirculation systems cannot be removed with traditional mechanisms. Foam fractionation is used to remove and manage the build-up of these solids. This method, in which air introduced into the bottom of a closed column of water creates foam at the surface of the column, removes dissolved organic compounds by actually adsorbing on the rising bubbles. Fine particulate solids are trapped within the foam at the top of the column, which can be collected & removed. The major factors affected by the operational design of the foam fractionators are bubble size and contact time between the air bubbles and dissolved organic compounds. Foam fractionation is a suitable process in seawater as well as fresh water & the efficiency is increasing with increasing salinities. That is related to the increased surface tension, allowing smaller air bubbles in seawater & there with a higher filter area. Foam fractionation is working efficiently from the salinity of 12ppm and more.


Reoxygenating the method of water is a crucial part of obtaining high production densities. Fish need oxygen to metabolize food and grow, as do bacterial communities in the biofilter. Dissolved oxygen levels can be increased through two methods aeration & oxygenation. In aeration air is pumped during an air stone that creates small bubbles in the water column, this results in a high surface area where oxygen can dissolve into the water. In general, due to slow gas dissolution rates & the high air pressure required to make small bubbles, this procedure is considered inefficient & the water is instead oxygenated by pumping in pure oxygen. Various methods are used to make sure that during oxygenation, all of the oxygen dissolves into the water column. Careful calculation & consideration must be given to the oxygen demand of a given system, and that demand should be met with either oxygenation or aeration equipment. 

Ultraviolet light:

UV disinfection works by affect light in wavelengths that destroy DNA in biological organisms. In aquaculture, pathogenic bacteria & one-celled organisms are targeted. The treatment has been used for medical purposes for decades & does not impact the fish as UV treatment of the water is applied outside the fish production area. It is important to understand that bacteria develop so rapidly in organic matter that controlling bacterial numbers in traditional fish farms has limited results. UV lighting used in aquaculture must work underwater to give maximum efficiency; lamps fitted outside the water will have no effect since of water surface reflection.


The use of ozone (O3) in fish farming has been criticized since the effect of over-dosing can cause severe injury to the fish. In farms inside buildings, ozone can be harmful to the people working in the area as they may inhale too much ozone. Thus, correct dosing & monitoring of the loading together with proper ventilation is crucial to reach a positive & safe result.

Ozone treatment is an efficient way of destroying unwanted organisms by the heavy oxidation of organic matter & biological organisms. In ozone treatment technology, microparticles are broken down into molecular structures that will bind together again & form larger particles. By this form of flocculation, microscopic suspended solids too small to be caught can now be removed from the structure instead of passing through the different types of filters in the recirculation system. This technology is referred to as water polishing as it makes the water clearer and free of any suspended solids and possible bacteria adhering to these. This is particularly suitable in hatchery and fry systems growing small fish, which are sensitive to microparticles and bacteria in the water.

Ozone treatment can be used when the intake water to a recirculation system needs to be disinfected. It is worth mentioning that in many cases UV treatment is a good & safe alternative to ozone.

Aeration systems

The efficient aeration devices move water into contact with the air. The normally used air stones produce larger air bubbles which rise quickly to the surface & hence the dissolution of oxygen is low. So, the usage of air diffusers is preferred in recirculating aquaculture systems. These diffusers make small air bubbles within the tank that rise through the water column. The smaller the bubbles & the deeper the tank, more oxygen are transferred.


After the settleable and suspended materials are removed by mechanical filtration, the next procedure was the removal of the dissolved ammonia, which came from the waste excreted into the water & uneaten fish feed particles. The general biofilters requirements are as follows:

  • Dissolved oxygen not less than 2 mg/liter or 3 to 5 mg/liter & this is for maximum efficiency;
  • pH level of 6 to 9.5. For Balancing pH, the pH level of the water must be maintained to a balanced ratio for ensuring the fish to survive well. The tolerable range of the pH level is between 6 and 9.5. pH of the RAS fish farming system can be maintained by adding buffers like sodium bicarbonate & calcium bicarbonate.
  • A supply of alkalinity for the buffer as vitrification produces acid which destroys about 7 mg of alkalinity for every mg of NH3- N oxidized;
  • Moderate levels of organic waste, and therefore good clarification is essential; and Water flow velocities that do not eliminate bacteria.


The procedure of detoxifying ammonia is called nitrification. Converting ammonia nitrogen to less toxic nitrogen dioxide & finally to non-toxic nitrate through bacterial action is the principal of nitrification.


The end product of nitrification procedure is nitrate and is non-toxic in nature, but the presence of nitrate beyond 100 mg has a negative impact on the growth of the fish & feed conversion. Supplying fresh water regularly to the tank can stay the levels of nitrate low. But the main aim of a recirculating system is to keep or lower the water consumption rate. Therefore a procedure called de-nitrification is adopted.

The de-nitrification procedure is required if the supply of water is less than 300 liters per kg of feed. The minimum amount of methanol necessary for de-nitrification is 1 kg of nitrogen is about 2.5 kg. The de-nitrifying chamber is fitted to the biofilter with the residence time of two to four hours.

Feeding the fish in the RAS system

You should provide feed in accordance with the growth, body weight & activity of your fish. On average must feed your fish with 4%-5% food daily of their total body weight. For example, if the total body weight of the fishes is 100 kg, then you must provide your fish with 4 to 5 kg foods daily. Provide the feeds twice a day. 2 to 2.5 kg at morning & another 2-2.5 kg during the evening. Always try to feed the fish with high quality feeds. You can purchase the ready-made commercial fish feeds.

Fishes suitable for RAS fish farming:

Recycled water is very much warmer than natural water. And cold water fish species such as salmon are not good for the RAS fish farming process. Barramundi, carp fishes, perch, catfish, white fish, tilapia, bluefin tuna, rainbow trout, seabass, and sturgeon are very good for the RAS fish farming system.

Stocking density in RAS system

It is important to maintain the production of fish in line with the capacity of the RAS fish farming system. Many methods are used for avoiding overloading of the method with heavy stocking density. Some of the methods are;

  • The fingerlings are not developed to market size fish in the same tank. Instead, you must use separate tanks.
  • The fishes grown to an intermediate size are graded & moved to another tank.
  • Before introducing the fingerlings into growth scheme tanks, quarantine tanks are used for them. Both quarantine & growth tanks are physically isolated.

Monitoring and controlling

Fish farming can be properly done only if there is a regulated control & monitoring system within the RAS fish farming system. A central system for controlling certain features like oxygen levels, pH range, water levels & other functions is deployed for efficient handling of the system. Install and use automatic sensors or alarms for indicating when a problem arises.

Cost of RAS:

Usually, the price of the RAS system depends on the area of setup. On an average for small Recirculating Aquaculture System costs approximately – Rs 3 Lakh/Unit

Some advantages of RAS fish farming

  • This process can achieve an optimal growing environment. This creates a stable & predictable production basis 365 days a year.
  • RAS addresses the growing demand for greener, cleaner, safer, transparent & more sustainable methods of growing fish.
  • Low water condition as the large majority of the water is cleaned then recirculated.
  • Significant reduction in disease due to the capability of the operator to control all aspects of the fish rising.
  • The fish are free from any Hormones and Antibiotics.
  • High production of quality fish in a relatively small area with a limited supply of water & land.
  • The flexibility to locate making facilities near large markets including “inland” locations and “food deserts.”

Read: Prawn Cultivation.


  1. I am Aqua Culture Technician, and I want to learn more about the Vannamei Culure and Recycling Aquaculture Systems Technique. Thank you,

  2. I want setup a RAS system within a budget of RS.3 lac/ unit. Guide me who are providing such setup. Please help me to setup my own unit.

  3. I am planning to set up a RAS system to produce 200 kgs fish in a 10 cubic metres tank .I need to know the type of filtration required and it’s cost ….within Rs.3. 00 lac per unit

  4. I have searched many sites . No one tells cost of RAS tank setup along with water purifying. we would like to know that what would be cost to set up RAS each tank


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