Yield Comparison and Efficient Use of Nitrogen in Two Aquaponic Systems

The fundamental principle of aquaponics is based on the nitrogen cycle, where fish waste ammonium (NH₄⁺) is transformed into nitrites and nitrates, which are absorbed by plants. However, when the pH is greater than 7, NH₄⁺ becomes ammonia (NH₃), which can be harmful to fish. In this regard, it was proposed to evaluate the effectiveness of two aquaponic systems consisting of a floating raft and a tezontle bedding in transforming ammonium into nitrates. Two production cycles were conducted. During the first cycle, significant differences among treatments were observed in the leaf area index (LAI), yield, and fresh weight of the lettuce (Lactuca sativa L.) plants. In the second cycle, differences were also found in dry weight, width, and length of the leaf (Tukey, α = 0.05). The lettuce yields obtained across treatments during the first production cycle were 3.7 and 3.96 kg m-2, while in the second cycle they increased to 4.05 and 6.8 kg m-2. Nitrogen use efficiency was 49.05 and 38.13 % in the first cycle and 57.86 and 36.6 % in the second cycle. Tilapia (Oreochromis niloticus L.) yields were 7.36 and 7.413 kg m-3. The results indicate that the tezontle bedding system was better in terms of yield and other performance indicators.