Acuoponia Basica

UPDATE ON TILAPIA AND VEGETABLE PRODUCTION IN THE
UVI AQUAPONIC SYSTEM
James E. Rakocy, Donald S. Bailey, R. Charlie Shultz and Eric S. Thoman
University of the Virgin Islands
Agricultural Experiment Station
RR 2, Box 10,000
Kingshill, VI 00850, USA

Abtract
The UVI commercial-scale aquaponic system has produced Nile and red tilapia
continuously for 4 years. During that time, two trialshave been conducted to evaluate the
production of basil and okra. Tilapia were harvested every 6 weeks from one of four 7.8-m3
rearing tanks. Nile and red tilapia were stocked at 77 and 154 fish/m3, respectively. During
the last 20 harvests, production of Nile and red tilapia averaged 61.5 and 70.7 kg/m3,
respectively. Mean harvest weight was 813.8 g for Nile tilapia and 512.5 g for redtilapia.
Nile tilapia attained a higher survival rate (98.3%) and a lower red conversion ratio (1.7) than
red tilapia (89.9% and 1.8, respectively). Projected annual production is 4.16 mt for Nile
tilapia and 4.78 mt for red tilapia. Batch and staggered production of basil in the aquaponic
system was compared to field production of basil using a staggered production technique.
Annual projectedyield of basil is 25.0, 23.4 and 7.7 kg/m3 for batch, staggered and field
production, respectively. Annual projected yield of basil for the aquaponic system is 5.34 mt
for batch production and 5.01 mt for staggered production. However, batch production was
not sustainable with the current fish output because nutrient deficiencies occurred. The okra
trial compared the production from threevarieties (Clemson, Annie Oakley and North South)
and two planting densities (2.7 and 4.0 plants/m2) in the aquaponic system. One variety
(Clemson) was cultivated in a field plot at the low planting density. The highest production
(3.04 kg/m2) was attained by the variety ‘North South’ at the high density.
Projected annual production of ‘North South’ is 13.37 kg/m2 and 2.86 mt per system.
Field okragrew slowly and produced only 0.15 kg/m2. The aquaponic system performed
well over a sustained period of time. Aquaponic production of basil and okra was
dramatically higher than field production.
Introduction
Aquaponics is the combined culture of fish and plants in recirculating systems.
Nutrients, which are excreted directly by the fish or generated by the microbial breakdown of
organicwastes, are absorbed by plants cultured hydroponically (without soil). Fish feed
provides most of the nutrients required for plant growth. As the aquaculture effluent flows

through the hydroponic component of the recirculating system, fish waste metabolites are
removed by nitrification and direct uptake by the plants, thereby treating the water, which
flows back to the fish-rearing componentfor reuse.
Aquaponics has several advantages over other recirculating aquaculture systems and
hydroponic systems that use inorganic nutrient solutions. The hydroponic component serves
as a biofilter, and therefore a separate biofilter is not needed as in other recirculating systems.
Aquaponic systems have the only biofilter that generates income, which is obtained from the
sale of hydroponicproduce such as vegetables, herbs and flowers. In the UVI system, which
employs raft hydroponics, only calcium, potassium and iron are supplemented. The nutrients
provided by the fish would normally be discharged and could contribute to pollution.
Removal of nutrients by plants prolongs water use and minimizes discharge. Aquaponic
systems require less water quality monitoring than individualrecirculating systems for fish or
hydroponic plant production. Aquaponics increases profit potential due to free nutrients for
plants, lower water requirements, elimination of a separate biofilter, less water quality
monitoring and shared costs for operation and infrastructure.
A commercial-scale aquaponic system was developed at the University of the Virgin
Islands in St. Croix. The status...