Aquaponics: smart system for food production in smart cities

This study aimed to test the rearing of common carp (Cyprinus carpio) at two stocking densities on water quality, fish growth and leaf vegetables (Cichorium intybus L. Catalogna group, Lactuca sativa L., and Beta vulgaris L.) yield in an aquaponic low-tech system compared to a hydroponic cultivation. Three treatments with three replications were studied: low fish density (AP1, 2.5 kg/m3), high fish density (AP2, 4.6 kg/m3) and hydroponic (HP). The trial lasted 133 days. The average daily evapotranspirated water from the systems was about 1.4% of the total (600 L). Fishes reached higher specific growth rates (0.79 vs. 0.68% d-1; P<0.001) and final body weights (516 vs. 413 g; P<0.05) in AP1 than AP2 treatment. However, the biomass production increased with increasing stocking density (4.45 kg/m3 vs. 6.88 kg/m3 for AP1 and AP2, respectively; P=0.01). On average, the highest total vegetables production was obtained in AP1 treatment (10.1 kg/m2) followed by HP (9.1 kg/m2) and AP2 (7.1 kg/m2) (P<0.05). The vegetables produced in aquaponic systems had a higher glucose content (+28.4%) than HP treatment, regardless of fish density. Water O2 content did not change among crop cycles in the HP treatment, while it decreased as fish load increased. The water NH4-N content was always below the thresholds for the reared fish. Our data show the fundamental importance of fish load in aquaponic systems suggesting that, in the proposed low-tech system, an initial fish density of 2.5 kg/m3 is suitable.