Aquaponics is an integrated fish and plant production technology. There are three distinct groups of people adopting this technology: new entrants, existing hydroponic operators and existing recirculating aquaculture system (RAS) operators. The potential for increased income is common to the interests and driving motivations of each group but other motivations, specific to the origin of the discipline involved, are also present. Existing hydroponic operators are primarily interested in accessing an organic nutrient solution for their plants, existing RAS operators are interested in a waste treatment outcome that avoids issues associated with waste releases and new entrants are mainly interested in a localized, niche-scale food production business

The RAS approach has a long association with aquaponics because most early aquaponic researchers had an aquaculture background. Aquaponics was seen historically as a technical approach to treat RAS waste nutrient streams so environmental impacts could be avoided or the associated cost of effluent disposal could be reduced, with the plants seen as a bonus outcome with some potential for sale. Although this long association is clearly present, some RAS practitioners have not fully adopted an approach to aquaponic design and management where emphasis is placed on the efficient and optimized production of plants. Plants require broad mixtures and concentrations of many nutrients to grow efficiently. Research with standard hydroponic plant culture practices has demonstrated that aquatic-based plant culture is complex and requires management with a high level of attention to detail that ensures optimized and efficient plant growth.

For aquaponics to become economically successful, a good understanding of standard RAS-based fish culture is essential, but a good understanding of hydroponic plant culture is also required. If RAS scientists, engineers and operators are to adopt the aquaponic approach and provide knowledge, designs and expertise to develop an aquaponics industry, then they need to become more cognizant of plants and their requirements. This makes even more sense in the context of most aquaponic designs, which emphasize plant production, and that plants generate the majority of revenue in many situations.

What is Aquaponics?
The term aquaponics is an amalgamation of the terms aquaculture and hydroponics; with aquaculture generally referring to finfish culture and hydroponics referring to water-based terrestrial plant culture. Aquaponics generally is defined as the combined culture of fish and plants in an aquatic environment or the integration of tank-based fish culture with hydroponic plant production or some variation on these themes. Therefore, at its root, aquaponics must include an aquatic animal and a plant in the production system. This definition of aquaponics principally concentrates on the two associated technologies of recirculating aquaculture systems and hydroponic plant culture and therefore, is suggestive of, and associated with, the technologies themselves and the related hardware or equipment involved.

Aquaponics is not just about the technology or hardware involved but rather, like any integrated agriculture practice or method, is about the partitioning and sharing of nutrient resources between the fish and plants. Delving a little deeper into the aquaponic method, and exploring definitions most practitioners state and often laud, demonstrates that the aquaponic method commonly follows a similar conserved pathway. Fish are fed a complete feed, the fish incorporate some of the nutrients from the fish feed, the fish then produces solid and dissolved wastes, some wastes are converted by bacterial metabolic processes to nutrients available to plants and those nutrients are taken up and incorporated into plant tissue. The outcome is two products: fish and plants. As stated, this outlines a partitioning and sharing of nutrient resources between the initial source (feed), the initial user (fish), the intermediate converter (bacteria) and the tertiary user (plants). In the context of nutrient flow, aquaponics is less about technical hardware or equipment integration and more about a nutrient resource sharing process.

How Does Aquaponics Work?
The above outlined method, starting with the addition of fish feed and ending with the production of fish and plants, appears to be universally accepted. What is not universally understood by many working with conventional RAS is that plants rely on a far broader range of nutrients for healthy growth and production than simply nitrogen alone. For example, plants require relatively large amounts of hydrogen, carbon, oxygen, nitrogen, phosphorous, potassium and calcium, moderate amounts of magnesium and sulfur and small amounts of micronutrients. Hydrogen, carbon and oxygen are easily accounted for because they are provided by water itself and atmospheric gases. The question of where other nutrients come from in an aquaponic context is one that singularly defines the aquaponic process. It is the origin of these nutrients that defines aquaponic theory, justifies and supports different aquaponic methods and approaches, and provides the only true and complete pathway to the assigned advantages of aquaponics.

A New, More Indicative Definition of Aquaponics
The whole point of aquaponics, and the grounds on which it was originally developed several decades ago, is that waste nutrients produced by fish are used to produce plants, which means that water is efficiently used to produce two crops rather than one. The goal should be that associated nutrients (initially added as fish feed) are used efficiently so that as many of them as possible are used to produce consumable fish and plant products. Little if any nutrients should be wasted and released to the environment. Furthermore, additions of supplemental nutrients beyond fish feed should be as small as possible to optimize the complete use of fish wastes.

An analysis of any of the best, scientifically configured, field-tested aquaponic methods developed thus far demonstrate that at least 80 percent by weight (and often more) of the nutrients required for optimal plant growth are derived from fish waste alone. In this context, therefore, it seems pertinent to provide a more complete definition of aquaponics that is more reflective of the process: A system of integrated, tank-based, aquatic-animal (fish) culture and hydroponic plant culture wherein the majority of nutrients required for plant growth arise from wastes derived from feeding fish.

This definition does not include a requirement for an approach that uses water recirculation between fish and plant components. Therefore, aquaponic systems can include approaches ranging from fully recirculating to fully non-recirculating.

Read the rest of this article in the September 2015 issue of World Aquaculture Magazine here