Aquaponics system design and application can be considered a highly multidisciplinary approach drawing from environmental, mechanical, and civil engineering design concepts as well as aquatic and plant-related biology, biochemistry, and biotechnology.
System-specific measurements and control technologies also require knowledge of subjects related to the field of computer science for automatic control systems. This high level of complexity necessarily demands in-depth knowledge and expertise of all involved fields.
The biggest challenge in commercial aquaponics is its multi-disciplinarity, needing further expertise in economics, finance, and marketing. Thus, a high degree of field-specific insight in terms of both practical and in-depth theoretical knowledge is required.
This leads to an increasing level of complexity, which directly affects the efficiency factors of the running system. Some numerical trade-offs are recommended and outlined below in the interest of the highest efficiency and productivity. They include pH stabilization, nutrient balance, phosphorus, and pest management.
A crucial point in aquaponics systems is pH stabilization, as it is critical to all living organisms within a cycling system that includes fish, plants, and bacteria. The optimal pH for each living component is different. Most plants need a pH value between 6 and 6.5 to enhance the uptake of nutrients.
The fish species Tilapia (Oreochromis) is known to be disease-resistant and tolerant to large fluctuations in pH value with a tolerance between pH 3.7 and 11 but achieves the best growth performance between pH 7.0 and 9.0 . The nitrifying bacteria have a higher optimum pH, which is above 7.
Villaverde  observed that nitrification efficiency increased linearly by 13% per pH unit within a pH range between 5.0 and 9.0 with the highest activity of ammonium oxidizers at 8.2. Similar observations were made by Antoniou et al. , who report an overall nitrification pH of approximately 7.8. There are three major bacteria, for which optimal pH conditions are as follows: (1) Nitrobacter: 7.5 ; (2) Nitrosomonas: 7.0–7.5 , and (3) Nitrospira: 8.0–8.3 .
Based on these data, the highest possible pH value should be consistent with the prevention of ammonia accumulation in the system. Then, the ideal pH value for the system is between 6.8 and 7.0. Although root uptake of nitrate raises pH as bicarbonate ions are released in exchange , the acidity-producing nitrification process has a higher impact on the overall system pH, leading to a constant and slight decrease in the pH value. There are two approaches to counteract that trend:
(1) Nutritional supplementation is the most applied method in use. By adding carbonate, bicarbonate, or hydroxide to the system, the pH value can temporarily be adjusted in line with the requirements. Also, they increase the alkalinity parameter that prevents large fluctuations in pH and thus keeps the system stable. The buffers should preferably be based on calcium, potassium, and magnesium compounds since they compensate for a possible nutritional deficiency of those essential nutrients for plants . Regarding the composition of the supplementation, it is important to seek a balance between those three elements.
(2) A proposed alternative approach is the implementation of the fluidized lime-bed reactor concept  into the field of aquaponics. This water neutralization concept consists of the controlled addition of dissolved limestone (CaCO3) to the acid water that leads to a continuous pH-elevating effect due to carbonate solubilization that releases hydroxide anions (OH−).
CaCO3(s) ⇌Ca2++ CO32−
Depending on pH, when CaCO3 dissolves, some carbonate hydrolyses produce HCO3−
CO32− + H2O ⇌HCO3− + OH−
The degree to which the pH is raised is dependent on the adjustable flow rate. However, this concept requires preliminary empirical measurements concerning the system’s steady pH drop to determine the size of the lime-bed reactor considering the specific flow rate.
As an innovative sustainable food production system, the challenge in aquaponics is to use the nutrient input efficiently, minimizing its discard and tending to a zero-discharge recirculating system [51,52]. Fish feed, the main nutrient input, can be divided into assimilated feed, uneaten feed, and soluble and solid fish excreta .
Soluble excreta are mainly ammonia and are the most available mineral until it is successively transformed into nitrite and nitrate by nitrifying bacteria [54,55]. Both uneaten feed and solid feces need to be solubilized from organic material to ionic mineral forms that are easily assimilated by plants. Minerals have different solubilization rates and do not accumulate equally [25,33], which influences their concentrations in the water.
All involved microorganisms and chemical and physical mechanisms of solubilization are not well understood [20,56]. Under current practices in RAS, the solid wastes are only partially solubilized as they are mechanically filtered out on a daily basis . These filtered wastes can be externally fully mineralized and reinserted into the hydroponic beds.
Given the objective of obtaining a low environmental footprint, a zero-discharge recirculating system concept should be achievable according to Neori et al. , but more research needs to be carried out on fish waste solubilization with the objective to transform all added nutrients into plant biomass.
There are two methods for mineralizing organic material that could be implemented: (1) anoxic digestion in special mineralization or settling units using bioleaching abilities of heterotrophic bacteria (e.g., Lactobacillus plantarum) ; and/or (2) using earthworm species such as Lumbricus rubellus capable of converting organic wastes to water enriching compounds in wet composting or grow beds .
Vermiculture can facilitate a high degree of mineralization as worm casts contain micro-and macronutrients broken down from organic compounds [60,61]. The addition of external sources (e.g., food waste) of feed for the worms to provide the aquaponic system with additional organic fertilizers has also been suggested .
Feed composition directly affects the nutrient excretion by fish, consequently affecting the water chemistry [33,63]. One challenge is to find the right fish feed composition for aquaponics in order to attain a water composition that is as close as possible to hydroculture requirements.
There is a need to establish the macro-and micronutrient proportion that fish can release in the water for a given feed in a given system; this depends on fish species, fish density, temperature, and type of plants (i.e., fruity plants or leafy greens). This will allow the prediction of the subsequent mineral addition needed to match optimal plant growth requirements.
Inorganic mineral input adds extra cost and issues for sustainable resource management (e.g., global P peak production reality) [12,13,14,64]. Thus, fish feed composition should be adapted to minimize this mineral addition while ensuring required nutrition properties for fish yield and avoiding phytotoxic mineral accumulation (e.g., Na). The fish feed origin regarding its environmental footprint should also be taken into account.
Low trophic fish species should be preferred and alternative production solutions should be promoted such as human food waste recycling , insects, worms, aquatic weed, and algae as a feed base [66,67]. Also, some fish–plant couples might be more appropriate than others in terms of overlap between nutrients profiles offered by excreta and nutrient profiles demanded by plants. Identifying these couples would assure the optimum use of the available nutrients.
A comparison of mineral concentrations in the published aquaponics literature (Table 3), with recommended recirculating hydroponics solutions leads to two main observations: (1) there is a lack of aquaponic data for some macro-and micro-elements, indicating the necessity of more research focus on them; (2) for the available data, the aquaponic concentrations are below the recommended hydroponic level.
However, Rakocy and Lennard (pers. comm.) report that hydroponics and aquaponics nutrient solutions are not comparable for many reasons. The nature of the total dissolved solids (TDS) is not the same in these systems. In hydroponics, TDS consists mainly of mineral compounds, while in aquaponics it includes organic molecules wherein nutrients can be locked up and overlooked by measuring procedures such as electrical conductivity (EC) or aqueous sample filtration.
Both aqueous sample filtration and the EC measurement methods only take nutrients that are available in ionic form into account. These suspended organic solids are assumed to promote growth because they might simulate natural growing conditions as found in soil, unlike the growing environment of hydroponics .
There is a lack of knowledge about the nature of organic molecules and the biochemical processes occurring for their assimilation by plants. Some can be taken up directly or need complex biodegradation to make them available.
Another difference is the microflora inherent to aquaponics while sterilization occurs in hydroponics. This microflora can have significant beneficial effects on plant growth and organic molecules assimilation. Hence, some aquaponics investigators report similar or even better yields than hydroponics for some crops, despite lower concentrations of mineral nutrients [1,71,72,73,74,75].
Voogt  identifies three aspects of the hydroponic nutrient solution composition that should be taken into account in aquaponics: (1) elemental uptake ratio compared to nutrient composition; (2) ease of uptake of specific elements; (3) the type of growing system that also requires a specific nutrient composition.
The composition of a nutrient solution must reflect the uptake ratios of individual elements by the crop, otherwise, it will lead to either accumulation or depletion of certain elements. As the demand between crops differs, the basic compositions of nutrients solutions are crop-specific . The uptake of elements differs widely, the absorption of some can be more difficult and necessitates relatively higher ratios than the straightforward uptake ratio of the crop.
The optimal nutrient levels for leafy and fruity vegetables in aquaponics systems are not yet well established. Additional research should be carried out to assess the optimum value of mineral concentration per single crop or hybrid multi-crop systems regarding growth rate and crop yield.
Optimal suspended organic solids’ levels should be identified with respect to their impact on vegetative growth. Also, a special emphasis should be placed on crop quality since productivity should not be the only argument for competitiveness.
For output purposes, this should be compared to (1) hydroponic crop grown with mineral nutrient solution; (2) conventionally soil-based agricultural methods; and (3) organic soil-based agricultural methods. Within-system comparative studies address productivity, as the macro-and micronutrient composition of the products will play a decisive role with respect to the future orientation of healthy and efficient quality food production.
A deeper understanding of the biochemical processes occurring in solid fish waste solubilization is necessary with the aim to increase mineral levels in aquaponic water by implementing process and specific waste biofiltration units.
Among the different minerals, phosphorus (P) deserves specific attention. It is a macronutrient, which is assimilated by plants in its ionic orthophosphate form (H2PO4−, HPO42−, PO43−). It is essential for both vegetative and flowering stages of plant growth . In RAS, 30%–65% of the phosphorus added to the system via fish feed is lost in the form of fish solid excretion that is filtered out by either settling tanks or mechanical filters [25,79].
Moreover, organic P solubilized as orthophosphate can precipitate with calcium (e.g., hydroxyapatite–Ca5(PO4)3(OH)) making these elements less available in solution [25,56]. Consequently, aquaponics experiments report a range of 1–17 mg L−1 PO4-P [24,31,32,38,70,80]. However, recommended concentrations in standard hydroponics are generally between 40 and 60 mg L−1 PO4-P [23,69,81]. This discrepancy suggests that phosphate should be added to aquaponic systems, especially for fruity vegetables that do not yet show satisfying yields in aquaponics .
Phosphorus is a finite and scarce mining resource and subsequently, an expensive component of hydroponic solutions. Sufficient phosphorus production will certainly be a major concern in the near future [12,14,64].
Therefore, solutions to reuse the discharge of P-rich effluents must be explored [83,84]. As up to 65% of P can be wasted in form of aquaculture effluent sludge, recovery solutions should be developed to achieve zero-discharge systems.
For example, leachate rich in P could be obtained by sludge digestion with selected P-solubilizing microorganisms  and then reinserted in the hydroponic part of the system. The ultimate objective is to develop a zero-discharge recirculating system with maximum nutrient recycling transformed into plant biomass and improved yield.
Pest and Disease Management
The challenges of pest and disease management is another aspect that needs further improvement . Aquaponic systems are characterized by a broader range of microflora than conventional hydroponic systems, especially because the breeding of fish and biofiltration occurs in the same water loop.
Conventional pesticides that are used in hydroponics cannot be used in aquaponics because of toxicity risk to the fish and to the desired biofilm (e.g., autotrophic nitrifying biofilm) . The need to maintain the nitrification biofilm and other nutrient solubilizing microorganisms also prevent the use of antibiotics and fungicides for fish pathogen control and removal in the aquatic environment.
Furthermore, antibiotics are not allowed for plant application so their use against fish pathogens must be avoided in aquaponic systems. These constraints demand innovative pest and disease management solutions for fish and plants that minimize impacts on fish and desired microorganisms.
Plant and fish pests and pathogens can be divided into four different categories based on specific alternative treatment solutions. These are (1) plant pests—mostly insects that damage the leaves and roots (e.g., aphids, spider mites); (2) plant diseases—microorganisms (e.g., bacteria, fungi) and viruses that attack plants; (3) fish parasites (e.g., monogenea, cestoda); and (4) fish diseases caused by viruses and microorganisms.
Rearing and crop practices that decrease the occurrence of diseases could be applied such as preventive sanitary measures, low density of fish and/or plants, and/or control of environmental conditions, which decrease relative humidity around the plants. In addition to these practices, a few innovative methods of biocontrol already exist for plants cultivated under field or greenhouse conditions.
These methods are based on the use of microorganisms with biocontrol activity [85,86], or extracts of such microorganisms or extracts of plants (including essential oils) that show high antimicrobial efficiency and short residence time [87,88].
It will be a challenge to select and adapt these methods to aquaponics systems, considering their compatibility with the other living organisms of the system. Furthermore, microbial diversity can be beneficial for plants. The presence of some mutualistic microorganisms in the plant biosphere can retard the development of pathogens [34,89,90] while promoting growth (e.g., plant growth-promoting rhizobacteria and plant growth-promoting fungi).
Since the presence of a broad range of microflora belongs to aquaponic practices, the occurrence of pathogens and risk for human health should also be established, in order to assess the safety of aquaponics and to conduct appropriate quality control. These challenges can lead to the production of products that are quality and pesticide-free certified (e.g., organic) and thereby achieve a higher price in the market and leads to a healthier population .
Other Technical Challenges
The regulation of the nitrate level in aquaponics is another challenge. Leafy vegetables need 100–200 mg L−1 of NO3-N concentration, while fruity vegetables need a lower level at species-specific growth stages . Intermittent intervals of high nitrate can be harmful to fish and nitrate concentration must stay under a certain threshold to avoid adverse physical effects to sensitive species (e.g., 100, 140, 250 mg L−1 NO3-N for Oncorhynchus mykiss, Clarias gariepinus, Oreochromis niloticus, respectively [92,93,94]).
Therefore, it is of particular relevance to determine the best practical means (BPM) fish: plant ratio before setup and/or implement a flow-controlled denitrification unit in the system in order to be able to adjust the desired nitrate level. Some denitrification tanks are already used in RAS , however, the technology is not yet fully developed.
The approach involves creating anoxic conditions in a column by using the sludge as an organic carbon source for heterotrophic denitrifying microorganisms and recirculates the nitrate-rich water through it. If anoxic conditions are applied in sludge, heterotrophic microorganisms are able to use nitrate instead of oxygen as an electron acceptor and reduce it successively to gaseous nitrogen (N2) . A critical step is to guarantee additional bio filtration before discharging the treated water back into the system to reduce the risk of toxic NO2− ions from the denitrification process entering the system.
Together with environmental conditions, population density is the most important parameter for fish well-being. In outdoor aquaponics facilities such as the UVI system, the common tilapia fish density without the use of pure oxygen is around 30–40 kg m−3. A higher density of up to 60 kg m−3 can be achieved in greenhouses ; this may be due to more algae and cyanobacteria blooms under longer daylight conditions, producing more oxygen from increased photosynthesis. These characteristics, however, cannot be generalized.
In fact, different fish species require different optimal water quality; e.g., warm water species tilapia require dissolved oxygen (DO) level of 4–6 mg L−1, whereas the cold water species trout needs at least 6–8 mg L−1 DO . Dissolved oxygen is not the only factor that needs to be kept stable. Large fluctuations in temperature and pH might harm fish, plants, and nitrifying microorganisms [98,99]. Despite this fact, temperatures for warm water species such as tilapia and nitrifying bacteria can be 25 °C–30 °C, whereas most plants rather prefer colder water temperatures (approx. 20 °C–25 °C).
Thus far, aquaponics has been built on a trade-off between the needs of fish and plants, respectively. Development is now needed to achieve optimal conditions for both fish and plants with either: (1) emphasis on interdependent parameters of both system components (e.g., combining fish and plant species that preferably require similar environmental conditions within the same range of temperatures and pH that ensure bacterial nitrification); or (2) the physical separation in two recirculating loops, i.e., an aquaculture and hydroponic loop, described as decoupled systems, where the optimal condition for each system is applied with periodic water exchange between them. These are different types of solutions that may contribute to the breakthrough of commercial aquaponics.
Aquaponics also responds to diverse ecological and social challenges, which point to the importance of focusing on efficient and sustainable forms of agricultural production. Socio-ecological challenges include mineral recycling, water scarcity, energy availability, overfishing, as well as urban farming, and short supply chains. They are outlined below.
In terms of sustainability, both phosphorus and potassium are major components of agricultural fertilizers, and like oil, they are non-renewable resources. Therefore, increasing use and depletion of these minerals without reuse or recapture has a negative impact on and is of significance to their future supply. This in turn would have dramatic consequences for global food security. Nutrient recycling policies, especially for phosphorus, are crucial in order to avoid global food shortages [12,14].
An increasing number of countries are facing economic and physical water scarcity, leading to growing incapability in feeding their people . On average, global agriculture uses around 70% of the available freshwater resources. In arid climate zones such as the Middle East and North Africa, agricultural water consumption can even be up to 90% .
Compared to conventional agriculture, aquaponics uses less than 10% of water, depending on the climatic conditions . Aquaponics can reduce freshwater depletion associated with irrigation whilst guaranteeing safe encouraging sustainable farming and food production practices, which in turn reduces freshwater consumption in countries facing water stress.
System-related water losses that occur in evaporation, plant transpiration, and the water content of the agricultural products can be compensated for by capturing water from air humidity  or by reverse osmosis desalination plants in coastal areas [104,105].
The energy requirements of aquaponics are likely to be based on system configuration (design, species, scale, technologies) and geographic location (climate, available resources). For each location, different measures are needed in order to ensure that each system will have a suitable sustainable energy source all year round to provide stable conditions for fish and plants.
This is crucial, as fluctuations in temperature might harm fish, plants, and nitrifying microorganisms [98,99]. This requirement constitutes a mandatory factor in regions with constantly and seasonally changing climatic conditions as well as in hot and arid climatic zones. Ensuring stable conditions may be achievable in equatorial areas without additional technology. Harnessing solar energy can be beneficial in order to either run climate control systems within greenhouses (e.g., via air conditioning operated by solar photovoltaic modules), or to heat up a low-energy greenhouse with passive solar heating .
The latter option is practicable for small-sized non-commercial (passive solar) greenhouses, but may not be suitable for larger greenhouses because of the high thermal resistance and high energy losses, associated with medium and large greenhouses. These larger structures may require alternative solutions. In countries such as Iceland and Japan, near-surface geothermal energy can be used by means of heat pumps and direct geothermal heat for maintaining the indoor temperature at the desired level [107,108].
Countries with comparatively unfavorable geological conditions still might assess possible options in terms of using waste heat of combined heat and power (CHP) units to heat the greenhouse during cold days  or cool them down during hot days. Those CHP units can mostly be found in combination with agricultural biogas plants, whereby surplus heat is fairly cheap for further disposal. Alternatively, they might consider using fish and plant species that are more suitable for the respective climatic conditions in order to avoid the expensive heating or cooling down of the system’s water.
Eighty percent of the world’s oceans are full- or over-exploited, depleted, or in a state of collapse. One hundred million tons of fish are consumed worldwide each year, providing 2.5 billion people with at least 20% of their average per capita animal protein intake . Fish is one of the most efficient animal protein producers, with a food conversion ratio (FCR) between 1 and 2 .
Since fish demand is increasing whilst the fishing grounds are overexploited , aquaculture is the fastest-growing sector of world food production . Adverse effects of this development include the high water consumption in the case of conventional fish protein production  and release of up to 80% of N and 85% of P per kg of fish feed [20,79] into the environment.
This causes the loss of valuable nutrients, resulting in eutrophication in rivers, lakes, and coastal waters, and excessive productivity leading to vast dead zones in the oceans . However, it has to be noted that high-protein fishmeal and fish oil are still key components of aquaculture feeds . Between 2010 and 2012, 23% of captured fish was reduced to fishmeal and fish oil . Decreasing the proportion of both fishmeal and fish oil in fish feed is thus a challenge that needs to be addressed.
Urban Farming and Short Supply Chains
Aquaponic systems can be set up almost everywhere and have the potential to (sub-)urbanize food production. This could bring important socio-environmental benefits. Aquaponic farming plants could be implemented in old industrial neglected buildings with the advantages of re-establishing a sustainable activity without increasing urbanization pressure on land.
Roof gardens would be another possibility, allowing the saving of space in urban areas. If greenhouses are used on roofs, they can insulate buildings while producing food . Another important aspect is minimizing the distance between the food producer and consumer. The longer the supply chain, the more transport, packaging, conservation, and labor needed, leading to substantial decreases of resources and energy (e.g., up to 79% of the retail price in US conventional food distribution ).
Shortening and simplifying the food supply chains can drastically diminish their environmental impacts while providing cities with fresher products. This also allows the consumer to clearly identify his food origin [118,119]. Nevertheless, one should not underestimate the development of rural locations, where farmland is plentiful. As aquaponics can be considered a high-tech agricultural method, it is necessary to assure knowledge transfer in this field to maintain skilled labor forces.
The current literature cannot be used to critically assess and predict economic challenges; as presented in Table 2, only two economic sub-studies are available in the peer-reviewed literature [24,36]. At this early stage of scientific research, the main focus has been on technical aspects of aquaponics; financial figures held by private research entities are not shared with the public.
Furthermore, it is difficult to compare the two systems to determine which is better as information may not be available for all system parameters and outputs. For example, light intensity (lm) was not reported by Rakocy et al. , yet this is one of the major factors affecting plant growth and thus the harvested biomass. Overall, system costs can be measured in the cost per square meter, which is influenced by the complexity of the system and this is closely related to climatic and geographic conditions such as seasonal daylight availability, temperature extremes, and fluctuation of warmth and cold.
Also, dynamic costs such as maintenance costs (i.e., price per kWh and labor) and sales revenues in regional markets might differ, making it more difficult to make accurate economic evaluations. Even comparing the most expensive item within a system is difficult, as it differs per region and country (e.g., electricity prices, heat availability, etc.).
Consequently, there is no general optimal system, as the system must be adjusted to environmental conditions. Another approach could be to calculate the cost savings by comparing the cost of RAS and hydroponics separately to the same system and integrated into an aquaponic system, under the same environmental and market conditions.
Hence, Rupasinghe and Kennedy  calculated an improvement of the net present value of 4.6% in an integrated aquaponic system of lettuce and barramundi. Unfortunately, there are no other studies available for comparison.
Market prices, one of the major factors for profit, can greatly vary between countries for several (e.g., cultural, historical availability) reasons.
However, the profit margins will definitely be higher if the product manufacturing costs are low and the food distribution supply chain is short. The transport, packaging, and conservation of the food are time and energy-consuming, which has an effect on the additional costs and freshness of the products. In order to meet these problems, more urban and peri-urban fresh food production plants need to be implemented to guarantee efficient short food supply chains .
Rakocy  showed with respect to crop choice, leafy greens generally achieve higher profitability than fruity vegetables. In an initial economic analysis, given the University of Virgin Islands (UVI) system design, they had a profit margin with basil exceeding almost by a factor 4 of that of lettuce. This finding should be viewed with a degree of caution because of different domestic market dependencies.
Nonetheless, when addressing economic optimization, the three most important factors are (1) sustainability considerations, which, in the case of aquaponics, are interrelated with economic profits, since the reuse of resources should cut costs for the producer and for the customer; (2) technical optimization of processes (e.g., nutrient availability in different growth stages, nutrient recycling, etc.), and; (3) system components (e.g., design of the hydrological regime, P recycling unit, pH stabilizing reactors, etc.).
Although Vermeulen and Kamstra  state that the actual perceived environmental benefits of nutrient reuse, energy efficiency, and land use seem only marginally cost-effective, the aspects of possible differences in product quality and societal value are not necessarily reflected in business costs. Also, the use and cost of fertilizers in hydroponic production systems has increasing importance, as fertilizer costs lie between 5% and 10% of the overall costs, and scarce fossil fuels are required in their manufacture .
The costing forecasts for fossil fuels could exacerbate the situation further and increase the demand for alternative fertilizer solutions such as. Another resource that becomes increasingly scarce is fresh water. Reprocessing instead of discharging contaminated water will be a big challenge that needs to be met in the future. Taxes for wastewater discharge or strong limitations in discharge by local or national policies might become a factor as all point source discharges are regulated by water quality policies. Anticipating this trend will ensure economic and financial advantages with respect to conventional agriculture or hydroponic approaches.
Education as a Necessity
A broad range of knowledge is required to understand and implement the multidisciplinary concept of aquaponics. From the theoretical perspective, the multidisciplinarity of the field and a lack of training in holistic thinking is a hurdle to fully comprehend the concept of aquaponics covering all interrelating issues. The bundling of field-specific in-depth knowledge is required in order to consolidate available scientific knowledge and evidence.
At most universities, the two main disciplines, i.e., hydroponics and aquaculture, are either not taught, or offered in different schools, which could complicate access and exchange of knowledge. In practice, aquaculture and hydroponic technologies are well-known. The problem lies in the fact that those disciplines need to be connected. This lack of information-sharing shows the necessity for developing an education network dealing with the improvement of the interconnection between (scientific) disciplines involved in this field.
Aquaponic stakeholders, including researchers, entrepreneurs, and technicians, need to have basic knowledge covering all disciplines that are involved in this field. Furthermore, experts within every connected field are required to address specific issues within theoretical, scientific, financial as well as practical frameworks.
Source: Goddek, S., Delaide, B., Mankasingh, U., Ragnarsdottir, K. V., Jijakli, H., & Thorarinsdottir, R. (2015). Challenges of sustainable and commercial aquaponics. Sustainability, 7(4), 4199-4224.