Managing Systems for Tilapia Culture
Tilapias (Oreochromis spp.) are increasing in popularity with consumers, and a number of fish producers in the United States are culturing them. During winter months in Alabama, surface water temperature falls too low for tilapia survival. Broodstock may be overwintered in waters heated by geothermal, solar, or mechanical means with spawning, nursery, and grow-out conducted during warm months. Alternatively, indoor culture systems with heating allow year-round culture, but energy for heating increases production costs.
Tilapia may be produced in tanks, raceways, cages, or open ponds. Although they are efficient filter feeders and use plankton for food, commercial feed is applied to increase production to profitable levels. Tilapia tolerate low dissolved oxygen and high ammonia concentrations better than most aquaculture species. Thus, they are stocked at high density, resulting in waters and effluents of culture units having high concentrations of nutrients, organic matter, and suspended solids.
Because of the necessity to provide supplemental heat to overwinter broodstock or to extend the grow-out period, water reuse systems are popular in temperate areas. Ground water in Alabama usually is warm enough to permit tilapia survival in winter. Thus, broodstock can be overwintered in tanks through which well water is passed. Placing tanks under transparent plastic covers can lessen the volume of ground water that must be applied to fish holding units. In warm months, the same units can be used to produce marketable-sized fish under more intensive conditions.
Because fish are stocked at high density in culture units, a large input of feed is necessary. Mechanical aeration or oxygenation maintains adequate dissolved oxygen concentrations, but water is flushed through culture units at a rate of several exchanges per day to prevent high concentrations of ammonia and other wastes. Solids which accumulate on bottoms of culture units are removed periodically via a center drain (Figure 1) or by other means.
Water flushed from grow-out units must be treated to improve its quality and especially to remove suspended solids and ammonia before being reused. Suspended solids and other pollutants also should be removed from water discharged during tank cleaning before it is reused or treated and released into State waters. A popular treatment procedure for culture unit effluent is to direct it through a basin or wetland for sedimentation and to hold it for several days in an open pond to allow natural physical, chemical, and biological processes to improve its quality for reuse (Figure 2). Water reuse systems with more complex treatment schemes as illustrated in Figure 3 also can be used in tilapia culture. The intermittent effluent from such systems should be treated through a properly designed and maintained sedimentation basin before discharge into State waters.
Treatment ponds should be designed and managed to minimize overflow. Solids removed from ponds have high organic matter content and should be managed according to NRCS technical standards and guidelines.
Procedures for pond culture of tilapia are the same as those used in channel catfish culture. Fingerlings are stocked in ponds, feed is applied, and mechanical aeration is used to prevent low dissolved oxygen concentration. The main difference in pond culture of channel catfish and tilapia is the necessity to drain (recycle for reuse) and harvest tilapia ponds in the fall before onset of lethal cooler water temperatures.
Source: Auburn University and USDA-Natural Resources Conservation Service, Alabama Aquaculture Best Management Practice (BMP)
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