Fish farming is one of the fastest-growing sectors of American agriculture.
Fish farming is one of the fastest-growing sectors of agriculture in the United States. Though there are several different kinds of fish farms, a recirculating aquaculture systems, or RAS, is well-suited to help meet the nutritional needs of the world's population. Defined, RAS is a high-density method for growing fish comparable to the broiler house in the poultry industry or the swine barn in the pork industry.
Holding Tank
The holding tank is the container that houses the growing fish. Sizes are determined by the available space, species size, desired density and the desired output of the farm. The tanks may be rectangular, circular or in a configuration called a "D-end Raceway." The D-end raceway is basically an oval shape with a dividing wall. In general, the term raceway is defined as a channel or tank with a continuous flow of water, a definition that fits the different types of RAS holding tanks.
Filtration
Bacteria is used to break down fish wastes.
Two types of filtration are required by an RAS fish farm: mechanical filtration and biofiltration. Mechanical filtration is one of at least two components intended to remove suspended solids from the water. Biofiltration is the process of removing the products of the fish's metabolic waste, such as ammonia and nitrites, from the system. Filters, which contain bacteria that break down this waste, usually have a large surface area that's conducive to bacteria growth.
Clarifier Tank
Besides mechanical filtration to remove suspended solids, a clarifier is used for the same purpose. It is a settling basin designed to concentrate and remove suspended solids before they clog the biofilters or consume too much dissolved oxygen. It is separate from the fish tank and the biofilter in order to allow for periodic cleaning. The addition of various filters can increase the clarifier's efficiency.
Aerators and Temperature Control
Water's capacity to hold dissolved oxygen depends on its temperature.
Maintaining the dissolved oxygen content of the water at optimal levels for the fish species in question is critical for their health. It is also important for the bacteria in the biofilters. Forced air aeration is sometimes used, but oxygen injection is more effective. In addition, the temperature of the water determines its capacity to hold dissolved oxygen. For this and other biologically important reasons, it is necessary to maintain the temperature of the water in an optimal range. This is accomplished through the use of heat exchangers, electrical immersion heaters, chillers or heat pumps.
Water Circulation Pump
Because the "r" in RAS stands for recirculating, pumps are an integral part of this type fish farm. Two basic types are used for recirculating the water: centrifugal impeller pumps and axial flow pumps. A centrifugal impeller pump consists of an impeller, or blade, inside the pump housing that turns and forces the water out the discharge. An axial flow pump consists of a propeller inside a pipe driven by a motor inside or outside the pipe.
