The classical working principle of aquaponics is to provide nutrient-rich aquacultural water to a hydroponic plant culture unit, which in turn depurates the water that is returned to the aquaculture tanks. A known drawback is that a compromise away from optimal growing conditions for plants and fish must be achieved to produce both crops and fish in the same environmental conditions. The objective of this study was to develop a theoretical concept of a decoupled aquaponic system (DAPS), and predict water, nutrient (N and P), fish, sludge, and plant levels. This has been approached by developing a dynamic aquaponic system model, using inputs from data found in literature covering the fields of aquaculture, hydroponics, and sludge treatment. The outputs from the model showed the dependency of aquacultural water quality on the hydroponic evapotranspiration rate. This result can be explained by the fact that DAPS is based on one-way flows. These one-way flows results in accumulations of remineralized nutrients in the hydroponic component ensuring optimal conditions for the plants. The study also suggests to size the cultivation area based on P availability in the hydroponic component as P is an exhaustible resource and has been identified one of the main limiting factors for plant growth.

Hydroponic systems and water management in aquaponics: a review

Nutrients that are contained in aquaculture effluent may not supply sufficient levels of nutrients for proper plant development and growth in hydroponics; therefore, they need to be supplemented. To determine the required level of supplementation, three identical aquaponic systems (A, B, and C) and one hydroponic system (D) were stocked with lettuce, mint, and mushroom herbs. The aquaponic systems were stocked with Nile tilapia. System A only received nutrients derived from fish feed; system B received nutrients from fish feed as well as weekly supplements of micronutrients and Fe; system C received the same nutrients as B, with weekly supplements of the macronutrients, P and K; in system D, a hydroponic inorganic solution containing N, Ca, and the same nutrients as system C was added weekly. Lettuce achieved the highest yields in system C, mint in system B, and mushroom herb in systems A and B. The present study demonstrated that the nutritional requirements of the mint and mushroom herb make them suitable for aquaponic farming because they require low levels of supplement addition, and hence little management effort, resulting in minimal cost increases. While the addition of supplements accelerated the lettuce growth (Systems B, C), and even surpassed the growth in hydroponic (System C vs. D), the nutritional quality (polyphenols, nitrate content) was better without supplementation.

Aquaponics is a production system based on the dynamic equilibrium between fish, plants, and microorganisms. In order to better understand the role of microorganisms in this tripartite relationship, we studied the bacterial communities hosted in eight aquaponic and aquaculture systems. The bacterial communities were analyzed by 16S rRNA gene deep sequencing. At the phylum level, the bacterial communities from all systems were relatively similar with a predominance of Proteobacteria and Bacteroidetes. At the genus level, however, the communities present in the sampled systems were more heterogeneous. The biofilter samples harbored more diverse communities than the corresponding sump samples. The core microbiomes from the coupled and decoupled systems shared more common operational taxonomic units than with the aquaculture systems. Eventually, some of the taxa identified in the systems could have beneficial functions for plant growth and health, but a deeper analysis would be required to identify the precise functions involved in aquaponics.

Aquaponics (AP) is a food production system that combines hydroponic (HP) crop production with recirculating aquaculture. Different types of hydroponic systems have been used for growing crops in aquaponics. However, very few studies have compared their suitability and efficiency in an aquaponic context. The study presented here compares tomato yield, morphological (external) and biochemical (internal) fruit quality, and overall tomato plant vitality from three different HP systems (nutrient film technique, drip irrigation system, and floating raft culture) and examines the distribution of nutrients in different parts of the tomato plant. Three replicate AP systems were set up, each incorporating the three different HP systems coupled with a separate recirculating aquaculture unit growing Nile tilapia. The results showed that the choice of the cultivation system had little influence on most of the above-mentioned properties. Tomato fruit mineral content was found to be in similar range for N, P, K, Ca, Mg, Fe, and Zn as reported in the literature. Yield and fruit quality were similar in all three systems. However, the drip irrigation system did perform slightly better. The slightly higher oxygen radical absorbance capacity (ORAC) of the fruits grown in AP in comparison to commercially produced and supermarket derived tomatoes might indicate a potential for producing fruits with higher health value for humans.