Nowadays, agriculture must face a new challenge: produce more food with fewer natural resources. To achieve this goal, scientists are testing a technique called aquaponics. Aquaponics was introduced many years ago by ancient Chinese and Mexican populations. In aquaponics, fish and plants are farmed together. How is this possible? Bacteria change the fish poop into nutrients useful for the plants. The plants take up these nutrients and clean the water, which can then be reused to farm the fish, and the cycle restarts! Aquaponics allows farmers to obtain two products at once, and to recycle the same water many times. Almost no wastewater is released into the environment! Aquaponics systems can have different sizes and do not need soil. They can be installed in both outdoor and indoor environments. Big aquaponic systems are used for commercial purposes, while small aquaponic systems can be used for urban farming—growing food within cities.
What Is Aquaponics?
The population of the world is increasing rapidly, and there is not enough food to feed this growing population! Scientists have an important mission: they must find a method for producing more food without stressing the environment. Traditional farming techniques damage the environment in many ways. They harm natural resources and pose health risks to humans and wildlife. A technique called aquaponics could be a solution to this problem. The “aqua” part of this word comes from aquaculture, which is the practice of raising fish, shrimp, algae, and other seafood. The “ponics” part comes from hydroponics, which is the cultivation of plants in water, without soil. Aquaculture and hydroponics can exist separately, but when we combine them, we obtain aquaponics!
Aquaponics is a miniature version of a natural ecosystem. It works the way Mother Nature normally works in every aquatic environment! First, in aquaponics, we put the fish to work. By working, we mean eating and pooping. This results in water that is rich in nutrients—yes, the fish poop! Then, bacteria come into play. Bacteria convert the fish poop into a perfect fertilizer for plant growth. The plants take up this fertilizer with their roots and, in doing so, also clean the water. The clean water is reused for farming the fish (Figure 1). The cycle restarts!
In an aquaponics system, fish, plants, and bacteria work together as a team. This teamwork allows farmers to obtain two food products, fish and vegetables, using the same amount of water that would normally be used to obtain just one product. In this closed cycle, water is not wasted—the wastewater released into the environment is almost zero !
Aquaponics, Past and Present
The idea of aquaponics is quite old. The first forms of aquaponics were used about 1,500 years ago, in South China, Indonesia, and Thailand. The farmers there grew rice in paddy fields that also had fish in them. The fish poop served as fertilizer for the growth of the rice plants (Figure 2).
Five hundred years later, a population in central Mexico invented another form of aquaponics. This population, known as the Aztecs, created a big empire. The capital of the empire, called Tenochtitlán, was built on the shores of Lake Texcoco. In that wetland, the Aztecs did not have fertile lands to cultivate their food. For this reason, they built gardens floating in the lake, called chinampas. These floating islands were made of mud and dried plant residue. On the chinampas, farmers cultivated maize, squash, tomatoes, and other crops. The plants could take up nutrients from the lake water, which was rich in fish poop.
Although the concept of aquaponics is ancient, it was not until the 1970’s that scientists rediscovered its potential. Nowadays, aquaponics is becoming quite advanced, and it provides a sustainable solution for agriculture, that will reduce the use of natural resources. Aquaponics uses up to 90% less water than traditional agriculture  and the plants grow much faster ! Aquaponics also reduces pollutants coming from the use of tractors and field chemicals .
Aquaponics systems can be installed both outdoors and in indoor, greenhouse-like environments. Indoors systems can allow food to be produced throughout the year! This is a great advantage in areas where the climate is not favorable for agriculture, for example, places with low temperatures, short daylight, and an absence of rain or freshwater for irrigation.
Types of Aquaponics
There are three main aquaponics systems in use today (Figure 3). In raft aquaponics, the plants are grown on floating rafts. The rafts float in tanks filled with the wastewater from the fish culture. The plant roots dip into the water where they can absorb the nutrients from the fish poop. This method is most appropriate for small plants like salad greens, basil, spinach, chard, and others. In substrate aquaponics, the plants grow in a substrate that mimics the soil. This substrate sustains the plant roots and helps the bacteria to filter the water. This kind of system is suitable for all types of plants, but it is most often used for cabbage, broccoli, onions, fennel, carrots, tomatoes, peppers, cucumbers, beans, peas, squash, and melons. Last, in channel aquaponics, the wastewater from the fish flows through narrow pipes with holes, into which the plants are placed. The roots dip into the stream of water within the pipe, where they can uptake the nutrients from the fish poop. This growing method works well for plants that need little support, such as strawberries, leafy greens, and herbs. The pipes can also be placed vertically to save space.
There are many fish species that can be used in aquaponics systems. These systems can incorporate large, small, edible, or ornamental fish, it depends on the ultimate purpose of the system. The most common species of fish in aquaponics systems are tilapia, bluegill, catfish, carp koi, fancy goldfish, shrimp, and pacu.
Benefits of Aquaponics in Cities
Nowadays, there is a growing interest in small-scale aquaponics systems. These systems can be located within cities; for example, they can be located in parks, urban gardens, buildings, houses, courtyards, and on rooftops. Introducing small aquaponics systems into cities can bring many benefits. Aquaponics can provide a large variety of organic and seasonal fresh produce. These vegetables are environmentally friendly because they have a reduced transport footprint—they do not need to be transported far before reaching our tables. Urban aquaponics systems can also encourage social initiatives. For example, they can promote cohousing and educational workshops, both of which provide people with a greater chance of meeting their neighbors. Aquaponics can also provide a shelter for birds and beneficial insects, which increases the city’s biodiversity . Last, urban aquaponics can help to create jobs for people in cities.
In summary, aquaponics is a circular soilless production system. It allows producing fish and vegetables together with the same amount of water, helping to save water. By participating in aquaponics, people can learn more about the lives of plants and fish. They can become more aware of how the foods they buy in grocery stores have been produced. This is especially important for younger people in cities and suburban areas, who are at risk of losing touch with the farming world. And one more important thing—participating in aquaponics is also a lot of fun!
Paddy Fields: ↑ A flooded field used to grow rice.
Raft Aquaponics: ↑ System in which plants are placed in holes drilled in rafts. The rafts float within tanks filled with fish wastewater. Plant roots dip in the water where they absorb nutrients.
Substrate Aquaponics: ↑ System in which plants are placed in holes drilled within pipes where continuously the fish effluent water flows. The roots dip into the water stream, where they can uptake the nutrients.
Channel Aquaponics: ↑ System in which plants are placed within a substrate that mimics the soil. This substrate also contains bacteria that help the plant to uptake nutrients from the fish wastewater.
Transport Footprint: ↑ Greenhouse gas emissions from transportation (trucks, airplanes, railways, etc.).
Cohousing: ↑ Communities in which people have their own residences but share common spaces such as rooftops, courtyards, and balconies.
Biodiversity: ↑ Set of all living forms that are on Earth—plants, animals, insects, fungi and micro-organisms, and their habitats.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The research leading to this publication has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 862663.
 ↑ Calone, R., Pennisi, G., Morgenstern, R., Sanyé-Mengual, E., Lorleberg, W., Dapprich, P., et al. 2019. Improving water management in European catfish recirculating aquaculture systems through catfish-lettuce aquaponics. Sci. Tot. Environ. 687:759–67. doi: 10.1016/j.scitotenv.2019.06.167
 ↑ Graber, A., and Junge, R. 2009. Aquaponic systems: nutrient recycling from fish wastewater by vegetable production. Desalination 246:147–56. doi: 10.1016/j.desal.2008.03.048
 ↑ Salam, A., and Prodhan, Y. 2014. Comparative growth performances of taro plant in aquaponics vs. other systems. Int. J. Innov. Appl. Stud. 7:941–6.
 ↑ Monsees, H., Suhl, J., Paul, M., Kloas, W., Dannehl, D., and Würtz, S. 2019. Lettuce (Lactuca sativa, variety Salanova) production in decoupled aquaponic systems: same yield and similar quality as in conventional hydroponic systems but drastically reduced greenhouse gas emissions by saving inorganic fertilizer. PLoS ONE 14:e0218368. doi: 10.1371/journal.pone.0218368
 ↑ Orsini, F., Pennisi, G., Michelon, N., Minelli, A., Bazzocchi, G., Sanyé-Mengual, E., et al. 2020. Features and functions of multifunctional urban agriculture in the global north: a review. Front. Sustain. Food Syst. 4:562513. doi: 10.3389/fsufs.2020.562513