Aquaponics is the combined culture of fish and plants in recirculating systems. Nutrients generated by the fish, either by direct excretion or microbial breakdown of organic wastes, are absorbed by plants cultured hydroponically. Fish provide most of the nutrients required for plant nutrition. As the aquaculture effluent flows through the hydroponic component of the recirculating system, fish waste metabolites are removed by nitrification and direct uptake by plants, thereby treating the water, which flows back to the fish rearing component for reuse.
The University of the Virgin Islands Aquaculture Program has developed a commercial-scale aquaponic system. The system consists of four fish rearing tanks (7.8 m3 each, water volume), two cylindro-conical clarifiers (3.8 m3 each), four filter tanks (0.7 m3 each), one degassing tank (0.7 m3), six hydroponic tanks (11.3 m3 each, 214 m2 of plant growing area), one sump (0.6 m3), and one base addition tank (0.2 m3). The system contains 110 m3 of water and occupies a land area of 0.05 ha. Major inputs are fish feed, water (1.5% of system volume daily on average), electricity (2.21 kW), base [Ca(OH)2 and KOH] and supplemental nutrients (Ca, K, Fe). The system can produce nearly 5 mt of tilapia along with 1400 cases (24-30 heads per case) of leaf lettuce or 5 mt of basil or a variety of other crops.
The UVI system represents an appropriate or intermediate technology that can be applied outdoors under suitable growing conditions or in an environmentally controlled greenhouse. The system conserves and reuses water, recycles nutrients and requires very little land. The system can be used on a subsistence level or commercial scale. Production is continuous and sustainable. The system is simple, reliable and robust. The UVI aquaponic system does require a relatively high capital investment, moderate energy inputs and skilled management, though management is easy if production guidelines are followed.