A series of experiments were conducted to evaluate the fish and vegetable production in a
recirculating aquaponic system In the first experiment, the efficiency of three
recirculating aquaculture systems (plant as a biofilter, a simple handmade- biofilter and
combination of both plant and biofilter) in the production of fish and removal of N-compounds
were evaluated. It was concluded that all the systems were efficient both in
the removal of N-compounds as well as giving high red tilapia (Oreochromis sp.) and
lettuce (lactuca sativa var longifolia) production. Within a period of fish culture (15
weeks), and a period of lettuce culture (5 weeks), the yield of red tilapia and lettuce
ranged from 13.61 to 19.41 kg/m3 and from 0.851 to 2.87 kg/m2 in the hydroponic area,
respectively. Based on the results of the first experiment, the system with the use of plant
as a biofilter was selected as a model for investigation of the nutrient removal and
reabsorption in an aquaponic system The main parts of the system consisted of a black
fiberglass tank (110L x 84 W x 100 H cm) equipped with three hydroponics troughs (110L x 30 W x 5 cm Depth), and a submersible pump (Model Aqua, 1500) for
recirculating the water through the culture system
In the second, third and fourth experiments, the total ammonia excretion by red tilapia
(the endogenous ammonia excretion related to catabolism of body protein and exogenous
ammonia excretion related to metabolism of feed protein), as well as gaseous ammonia
escape rate during different stages of its growth from the culture system were evaluated.
It was found that the weight of fish significantly affected ammonia excretion. The rate of
total N content of feed excreted by red tilapia ranged from 31.10 to 54.20% for 20-200g
red tilapia On average, 39.54% of the nitrogen content of fish feed was excreted as
ammonia-N by red tilapia. Water recycling influenced the escape of ammonia due to
ventilation an in the culture system. However, the rate of ammonia escaping from the
system, decreased inversely with an increase in the fish weight. The percentage of
escaped ammonia ranged from 7-72% of total ammonia excreted by fed fish
