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Outline

Aquaponics: Integrated Technology for Fish and Vegetable Production in Recirculating Systems James Rakocy University of the Virgin Islands Agricultural Experiment Station St. Croix, U.S. Virgin Islands

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Advantages of Aquaponics Fish provide most nutrients required by plants Plants use nutrients to produce a valuable by-product Hydroponic component serves as a biofilter Integrated systems require less water quality    monitoring than individual systems Hydroponic plants extend water use and    reduce discharge to the environment Profit potential increased due to free nutrients for plants, lower water requirement, elimination of separate biofilter, less water quality monitoring and shared costs for operation and infrastructure.

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Treatment Processes Air stones, 22 in rearing tank, 144 in hydroponic tanks Solids removal, three times daily from clarifier,    filter tank cleaning one or two times weekly Continuous degassing of methane, CO2 , H2S, N2 Denitrification in filter tanks Direct uptake of ammonia and other nutrient by plants Nitrification in hydroponic tank Retention time: rearing tank, 1.37 h; clarifier, 20 min,    hydroponic tanks, 3 h

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Production Management Feeding: three times daily ad libitum     32% protein, floating, complete diet Stagger production, 24 week cycle, 6 week harvest Stagger plant production, use biological insect control Monitor pH daily, maintain pH 7-7.5 by    alternate and equal additions Ca(OH)2 and KOH Add chelated iron (2 mg/L) every 3 weeks Daily makeup rain water, about 1.5%

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Production Tilapia - 5 mt annually , 580 kg every 6 weeks,    160 kg/m3/yr Stocking rate: Niles, 77 fish/m3; reds, 154 fish/m3 Leaf lettuce - 1,248 cases annually, 24-30 heads/case,  27 cases/week Basil – 5 mt annually

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Energy Consumption One blower for fish and degassing, 1 hp One blower for hydroponics, 1 hp One water pump, ½ hp Total energy consumption 2.5 hp

Important Principles Optimum feeding rate, 60 - 100 g/m2 plant area/day prevents nutrient accumulation or deficiency Slow removal of solids increases mineralization Frequency of filter tank cleaning controls    nitrate levels through denitrification Treatment capacity of hydroponic tanks is equivalent to 180 g of feed/day/m2 of plant area

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Research Needs Reduce capital costs by using inexpensive, locally available construction materials Determine production capacity of different fish and plants Assess site-specific economics of various fish/plant combinations.

Perspective on UVI Aquaponic System The system represents appropriate or intermediate technology It conserves water and reuses nutrients The technology can be applied at a subsistence level or commercial scale Production is continuous and sustainable The system is simple, reliable and robust Management is easy if guidelines are followed