The common components of all recirculating systems
In simple terms, the goal of a recirculating aquaculture system is to produce fish in a cost effective manner where the environment is controlled through water treatment and recirculation. Every system, regardless of size or complexity, has a common set of components and must deal with a common set of issues.
The following pdf publications from the Southern Regional Aquaculture Center provide relatively detailed information regarding the components and critical issues. For a general description follow the links in the table below.
SRAC 451 Recirculating Aquaculture Tank Production Systems: An Overview of Critical Considerations*
SRAC 452 Recirculating Aquaculture Tank Production Systems: Management of Recirculating Systems*
SRAC 453 Recirculating Aquaculture Tank Production Systems: A Review of Component Options*
* You will need Adobe Acrobat Reader to open these files. It is probably already installed on your computer. You can also download a free copy from Adobe Systems
Culture Tanks - are the containers, tanks, buckets, aquariums etc. that house the culture animals. Size requirements for the tanks will depend on several factors including, the species, adult size, desired culture density and available space. Tanks can range from small aquariums for tropical fish to 10,000 gallon tanks for large food fish. Tank shapes include round, rectangular, and D-end raceways (basically oval with a dividing wall). top
Solids Removal is the process of removing solid particulate matter from the systems. The bulk of these solids are in the form of feces or uneaten feed. These wastes generate the greatest amount of pollution in a closed system, so it is important to remove them as rapidly and as efficiently as possible. Solids can be broken into three categories. Settleable solids are those particles that will generally settle out of the water within one hour under still conditions. The large solids can be removed by well placed drains, a sedimentation tank (clarifier), mechanical filtration, or a swirl separator. Suspended solids are those small particles that will not settle to the bottom of the tank. These suspended solids can be removed by running the water through a fine screen or other form of mechanical filter such as a bead or sand filter. Fine and dissolved solids are very small particles less than 30 micrometers that require special equipment or management to remove. Top
Biofiltration is the process of removing dissolved metabolic waste products (ammonia and nitrite) from the water. This process requires the water to pass through filters that have live bacteria living in them. The filters are usually filled with small media with a large surface area where the bacteria can grow. The effectiveness of this process depends on the amount of bacteria that can be grown in the filter and maintaining optimum conditions for their survival. Top.
Oxygenation refers to the process of supplying oxygen to the system. Oxygen is critical not only to the culture animals but also to the bacteria in the biofilter. Most "low tech" RAS systems use diffusion of low-pressure air pushed through air stones in the culture tank for aeration. This method while inexpensive is not a very efficient means of adding oxygen to the water but for our purpose works very well. Other "high tech" commercial systems use pure oxygen injection. Top.
Water Circulation - Any "recirculating" system will require a pump or other water movement device to move the water through the system. To function efficiently and reliably, pumps must be carefully selected and integrated in to the system. There are many varieties of pumps each engineered with a specific application in mind. The two types of pumps most commonly found in aquaculture systems are centrifugal impeller and axial flow pumps. For more information on pump selection check out these links.Top.
Selection of Centrifugal Pumping Equipment
Temperature control - depending on the species being cultured and the location of the system some degree of temperature control will likely be necessary. For warm-water species such as tilapia, temperature control is critical. If water temperatures drop below 65 degrees the fish will likely get sick and/or die. Optimum temperatures of 80-85 degrees should be maintained for tilapia. For cold-water species like trout the water may have to be cooled with a Chiller. Temperatures can be regulated with electrical immersion heaters, gas or electric heating units, heat exchangers, chillers or heat pumps. The most popular types of heaters for small applications are immersion heaters or gas powered radiant heaters. For more information on temperature control look here. Top.
Fine and Dissolved solids are removed by a process called foam fractionation. This process has also been referred to as protein skimming or air stripping. The fine and dissolved organic compounds cling to the bubbles used in the process. This results in foam, which can then be removed, from the system. This fine and dissolved matter is also removed during water changes. For most "educational" systems changing some water regularly will help avoid problems with dissolved solids build up. For more information look here. Top.
Disinfection using ultraviolet irradiation or ozone are generally not required in educational systems. In commercial systems the high densities of fish can result in diseases which can spread quickly through the system. Chemical sterilization of a system works well but it requires starting from scratch because the chemical will kill the "good" bacteria in the filter as well as the "bad" disease causing bacteria or parasites. The process of running the water passed UV lights helps kill microorganisms that could cause problems in the system. For more information on disinfection look here. Top.
Feeding the fish is the most entertaining part of growing fish. Care must be taken, however, not overfeed because this is one of the major sources of "pollution" in the tank. The correct type and amount of feed is critical to optimum growth of the fish. In general tilapia do well on a 28-32% protein catfish feed. The size of the feed is also important, small fish will not do well on large pellets and much of the food will be wasted. Pellet size should accommodate the smallest fish in the system. Pellet size can be increased as fish grow. For more on feeding fish see the resources page. Top.
Disease Control - Prevention is the best medicine. Stress plays a major role in the development of disease. Make every attempt to avoid stressful situations. Poor water quality, mechanical stress (ie chasing and handling the fish) and overcrowding are the most likely sources of stress in these types of systems. If the fish do get sick there is very little that can be done with the exception of modifying the temperature or adding salt to the system. Using chemical or antibiotics might be helpful, but they also have serious side effects on the operation of the system. For more on fish diseases, control and treatment see the resources page. Top.
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