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Today, as a result of rapid population growth, increased food requirements and urbanization, the amount of agricultural land is rapidly declining and our oceans are overfished. To meet future demands for food, there is a need for innovative, space-saving, and ecological food production technologies. Aquaponics is a polyculture (integrated multi-trophic production system) consisting of two technologies: aquaculture (a fish farm) and soil-less (hydroponic) cultivation of vegetables. The primary goal of aquaponics is to reuse the nutrients contained in fish feed and fish faeces in order to grow crops (Graber & Junge 2009; Lennard & Leonard 2004; Lennard & Leonard 2006; Rakocy et al. 2003). The integration of two systems into one removes some of the unsustainable factors of running aquaculture and hydroponic systems independently (Somerville et al. 2014).
Figure 1: Basic material flows in aquaculture (a), hydroponic (b), and aquaponic (c) systems
Fish excrement can be used by plants either directly or after bacteria have converted the ammonia to nitrite and nitrate. The fish feed adds a continuous supply of nutrients to the plants, thereby solving the need for any discharge and replacement of depleted nutrient solutions or, in the case of extensively operated systems, the adjustment of the solutions as in hydroponics. As the need to buy additional fertiliser for the plant crop is reduced, the profit potential of the system increases. Aquaponics is a rapidly emerging agricultural practice that therefore offers a series of potential benefits; however, there are also major weaknesses to this potentially sustainable agricultural production system (Table 1).
Benefits Weaknesses Conservation of water resourcesEfficient use of nutrient source (fish feed) Recycling of non-renewable resources (like phosphorus, potassium) and also of renewable, but scarce, ones (like water) No use of chemical herbicides or pesticides, as the recycling of water within the system hinders their use due to their adverse effects either on the fish or on the plants Very restricted use of pesticides of biological origin Higher level of biosecurity and fewer contaminants Reduced operating costs (compared to aquaculture or hydroponics separately) Can be used on non-arable land Construction materials and information are widely available Can be operated in different climates and in both rural and urban locations, thereby enabling the production of family food or cash crops Can increase the productivity of the available space, because two crops can be harvested from the same surface area (if the fish tanks are placed below the plant production unit) The start-up is more expensive when compared to other technologies Thorough knowledge of the organisms (fish, plants, bacteria) involved is necessary The requirements of fish and plants can be different, and cannot be met in all locations without major investment in greenhouse technologies Daily management is necessary It requires electricity, supply of seedlings and fingerlings (young fish) In most European countries the legal status of aquaponics is unclear (business activity, agricultural activity)
In theory, the concept could contribute, on both a regional and a global level, to the solution of some of the crucial problems our planet is facing: availability and use of potable and irrigation water, pollution of surface waters through animal farming, and management of non-renewable fertilizer resources. However, there are still many theoretical and practical obstacles to the expansion of this promising technology.
Thus, aquaponics tends to be an ecological and climate-friendly method for producing nutritious food and, at the same time, for meeting consumer demand for a sustainable and healthy lifestyle. Provided that the investment is not too high, aquaponics is ideal for developing countries because the fish provide much-needed protein and a second source of income. High value cash crops, such as vegetables, can be grown with aquaponics in areas where conventional farming methods can only produce grains. Because the system is usually enclosed in a greenhouse, aquaponics is resistant to climate and weather changes. However, aquaponics has also been successfully implemented outdoors. For a less expensive option, the plants can be covered with a simple roof (that provides shelter from inclement weather and prevents the access of birds and other animals) rather than a full greenhouse. This is especially viable for developing nations in the tropics. In spite of weaknesses, aquaponics is thought to become a future production method for locally grown food, e.g. in an urban environment with smaller production units designed for homes and restaurants. Both research and education are needed in order to develop this emerging technology. In particular, research is needed to optimize the production system towards safe and economical production. The technique opens up new perspectives for creating new 'green jobs'. The increasing number of aquaponic farms will necessitate the rise of a new profession: the aquaponic farmer (Graber et al. 2014a).
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