4. Discussion
4.1. Fish and vegetable production in aquaponic
Fish production did not differ from typical
conventional aquaculture systems with tilapia
[4] and perch. The quality of the produced tomatoes
however was impaired by a lack of potassium.
As potassium is not needed by fish, it is
not added to fish feed and thus to the system in
adequate amounts. In later experiments, potassium
was supplied by adding KOH to stabilize
decreasing pH values due to permanent nitrification.
Tomato yield equalled productivity in traditional
soil cultures but was significantly
lower than in intensive soil-less cultivation.
With respect to the nutrient recycling capacity,
aquaponic systems could nevertheless be profitable
for vegetable producers. It was shown
before through computer modelling that combining
aquaculture and traditional agriculture
increases income while minimizing production
risks [27]. In Australia, several companies are
already applying the technique and are serving
the market with produce [5].