August 2013 Vol. 1 No. 1

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Full Length Research Paper

Recirculating aquaponic systems using Nile tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) polyculture and the productivity of selected leafy vegetables

Chito F. Sace, Ph.D.¹* and Kevin M. Fitzsimmons, Ph. D.²

¹Associate Professor, Institute for Climate Change and Environmental Management, Central Luzon State University, Science City of Munoz, Nueva Ecija, Philippines
²Professor, Extension Specialist, and Director of International Agricultural Programs, Soil, Water, and Environmental Sciences, College of Agriculture and Life Sciences, The University of Arizona, USA

*Corresponding Author’s E-mail: cfsace227@yahoo.com; Telefax +63 (44) 4565843; +63 (44) 4565188

Accepted August 19, 2013

Abstract

A study on the productivity of lettuce (Lactuca sativa), Chinese cabbage (Brassica rapa pekinensis) and pac choi (Brassica rapa) in a recirculating aquaponics system using Nile tilapia (Oreochromis niloticus) and fresh water prawn (Macrobrachium rosenbergii) polyculture was conducted in a controlled environment. The system was effectively designed by following the “one-pump rule” having the culture water lifted by a 40-watt submersible pump from the 200-L bio-filtration tank, the lowest portion, to the 250-L fish tank, the highest portion, allowing the flow of water by gravity along the 2.44 m x 4.88 m raceway and the over-sized return pipes in a closed loop. Hydroponically germinated seedlings in rock wool received foliar fertilizer daily for 12 days and were transplanted on the rafts at 15-cm spacing 30 days after stocking 22 kg of mixed-sex tilapia in the fish tank and 295 prawns in the raceway with 20-cm water depth to permit rafts to float. Fish were fed ad libitum with commercial feeds while excess feeds entered the raceway for the prawn to scavenge. Environmental conditions were maintained and water quality parameters were monitored in a compromise between the ideal requirements of fish, prawn and vegetables including the beneficial bacteria throughout the108-day culture period. Two sets of data for vegetables and one for tilapia and prawn were gathered after the two 35-day growing seasons of vegetables. Another similar system without prawn was installed as control and received the same cultural management from where similar data were gathered. The two systems provided favorable water quality for tilapia, prawn and nitrifying bacteria with average dissolved oxygen of 5.6 ppm at 98 per cent saturation and 21 ͦ C temperature. A pH of 7.1‒7.5was established and total dissolved solids of 250‒390 ppm were provided in the system with prawns while 7.4‒7.7 pH and 220‒350 ppm of total dissolved solids in the control. However, the low concentration of nutrients at high pH, which was far below the crop requirement, triggered the vegetables to exhibit nutrient deficiencies. Results uncovered that the stocking density of tilapia and the ratio of the aquaculture to the hydroponic components were inappropriate which limited the system to accumulate and increase the concentration of nutrients thereby causing chlorosis and necrosis among the vegetables and lessened the yield. Nonetheless, the system with prawns has higher nutrient content that vegetables demonstrated significantly better growth and yield than in the control which disclosed that integrating prawns helped stabilize and diversify the system thus improving yield. Among the three vegetables, pac choi had the highest growth and yield, followed by Chinese cabbage and lettuce. Tilapia also has higher gain in weight and better feed conversion ratio in the system with prawns. Prawns, likewise, has 6.42 g weight gain and 71 per cent survival rate. It was also confirmed that stocking density and component ratio were critical factors in designing aquaponic system.

Keywords: Aquaponics system, vegetable-tilapia-prawn polyculture, tilapia-prawn-vegetable recirculating system, aquaponics in a controlled environment, leafy vegetables production