Types of Aquaculture Systems for Farming Fish

There are many types of systems and farm designs used to grow fish. These include, ponds, net cages in lakes or oceans, rectangle raceway tanks, circular (round) tanks, earthen tanks lined with plastics and other forms of containment. Basic Land based fish farms involve the use of one or more types of tanks or ponds and generally have water piped in and out to maintain life support for the fish and to flush the tanks of waste products. Basic designs may also include mechanical aeration equipment for adding oxygen to water. In recent years land based farms have advanced in technologies to become more eco-friendly and to provide greater security and control of the farming process, these are known as water recirculation systems or RAS designs. 

Benefits of Recirculation Aquaculture System Designs

Fish grown in a RAS facility must be supplied with the correct conditions necessary to remain healthy and grow. They need a continuous supply of clean water at an appropriate temperature and a dissolved oxygen content that is optimum for growth. A mechanical and biological system is necessary to purify the water and 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 and high survival. With that in mind let's review the potential benefits of using farm systems based on RAS designs.

Low water Requirements

A properly designed and operated recirculating system requires a minimum daily input of water, just enough to clean the waste from the filters and to replace water lost to evaporation. This allows construction of fish farms in areas where ground water is limited and even opens the possibility of an operation being located in an urban area to use de-chlorinated municipal water. Such a production facility could be located close to the market. By comparison a recirculating system which produces the same number of pounds of fish as 1000 acres of ponds (about 4.8 million pounds of fish) would require about 4000 gallons of fresh water each day or 1.5 million gallons per year, However, to fill 1000 acres of ponds averaging 5 feet in depth would require 1.6 billion gallons of water.

Less Land Requirements

Since fish in a recirculating system are reared in tanks, with oxygen being supplied and their metabolic wastes removed by flowing water, fish can be be safely stocked and grown at high densities. Currently the goal which designers are striving to attain is 1 pound of fish per gallon of water. However, many people consider 0.5 to 0.75 pounds of fish per gallon of water acceptable, In pond aquaculture, the common maximum density is about 0.003 pounds of fish per gallon of water, Therefore, a recirculating system can be located in areas where large amounts of level land are not available. The low land requirement also permits the facility to be located in areas where the soil cannot hold water or, again, in urban areas, or housed in vacant warehouse buildings converted to fish farming.

Control of Water Temperature

The low water requirement of recirculating systems opens up the possibility of economically controlling temperature which, next to lower water quanity, is one the greatest benefits of these systems. Control of water temperature allows the aquaculturist to produce a fish species which could not normally be raised in a given geographic area. It also permits the water temperature to be maintained at the optimum level to maximize food conversion and provide optimum growth, Growth can also occur throughout the year, maximizing production and allowing rapid turnover of the product, In theory, marketing of the product is also enhanced, since fish can be supplied each week.

Independence From Elements

By rearing the fish indoors, the farmer is no longer limited by weather conditions where a sudden cold spell can wipe out a year's production by killing the larval fish or disrupting the normal spawning of the broodfish. In addition pond culturists can loose their crop to low oxygen during the summer or winter. Having the fish indoors also permits harvest at times when heavy rain, snow or ice would stop the harvest of pond fish; creating a definite market advantage.

Control of Water Quality

With recirculating systems, the aquaculturist has the opportunity to control water quality, both to the benefit of the live fish and to the final product. By maintaining dissolved oxygen at optimum levels, the fish have better food conversion and are less stressed, which translates into greater disease resistance. In addition, the fish are isolated from potential environmental contaminants such as off-flavor caused by some algal growth and from any potential pollution resulting from soil run-off or residual pesticides. This results in a high quality product. In many cases where the fresh water is supplied by wells the likelihood of disease outbreaks are greatly reduced and medications are not required.

There are various designs for recirculating systems and most will work effectively if they accomplish oxygen and aeration, removal of particulate matter, biological filtration to remove waste ammonia and nitrite and buffering of water pH levels. These processes can be achieved by simple units that use combination filter's in small farm systems, or in in the case of larger farms by several interconnected components and unit processes.

RAS systems also help make possible crop diversification with Aquaponics, which is the use of fish waste nutrients and water to grow other edible plant crops. This practice is in fact becoming more common and in some cases the plant crop production has a greater value than the fish crop.

If you are serious about water recirculation sytem design in Aquaculture, obtain a copy of Recirculating Aquaculture Systems from the Aquaculture Book Store. 

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