Recirculating systems
Concerns for water conservation and reduced waste discharges have prompted the increased use of closed recirculating aquaculture systems. Recirculating systems generally consist of land based tanks with constantly flowing water.
The systems are made up of three basic components: culture chamber, settling chamber, and biological filter. Water enters the culture chamber, flows through the settling chamber and then moves through the biological filter to remove additional particulate matter. The water is then circulated back through the systems’ culture chambers.
Recirculating systems conserve water and allow producers to control all of the environmental factors that might affect their plants and animals.
For example, aquaculturists have complete control over temperature, salinity, oxygen, predators and introduction and transfer of diseases. Recirculating systems, however, can be costly to operate, as they are highly dependent on electricity or other power sources.
Pumps must be used in order to maintain the constant flow of water and often water must be heated or cooled to the desired temperature. Backup systems must be in place in case of a power failure.
A less expensive and more environmentally friendly option would be to take advantage of alternative energy and heating sources.
Solar, wind and geothermal power are being considered as is heated water obtained from the waste products of manufacturing, electricity production, and composting.
For example, tilapia farms can use the cooling water from power plants as a low cost warm water source. The warm water, which is necessary for growing tilapia, would otherwise be wasted. Recirculating systems have less of an impact upon the environment because of their closed nature – wastes and uneaten feed are not simply released into the ambient environment in the manner that they are with netpens and exotic species and diseases are not introduced into the environment.
In recirculating systems, wastes are filtered out of the culture system and disposed of in a responsible manner. Recirculating systems can be built just about anywhere, including in urban settings where they can use existing structures and be placed close to markets, thereby reducing transportation costs.
Recirculating systems can be used to grow a wide variety of fish species year-round in controlled environments. Species commonly grown in recirculating systems include hybrid striped bass and tilapia. Additionally, much research has been dedicated to developing recirculating systems for marine species of fish and this technology holds much promise.
Inland pond culture:
Pond aquaculture was the earliest type of aquaculture to be practiced, dating back several thousand years. It remains one of the most common systems used to farm fish.
Over 75 percent of the farmed freshwater fish in China are produced in constructed ponds and in the U.S. nearly all of the farmed catfish are raised in ponds.
Other species commonly farmed in ponds include tilapia, hybrid striped bass, and crayfish. When properly managed with little or no water exchange, wastes are not continuously released from the culture system as they are in netpens or flow through systems.
Wastes, including solids, organic matter, and nutrients that are discharged can be released into settling ponds or constructed wetlands to further reduce their impact. In low or zero discharge pond systems, the pond itself develops a sort of ecosystem.
Natural biological, chemical, and physical processes in ponds remove much of the wastes from the water. Waste accumulation and subsequent discharge from ponds is minimal as long as production is maintained within the limits of the natural processes to remove or assimilate wastes.
Authors:
Kathryn White, Brendan O’Neill, and Zdravka Tzankova
