WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2015 21 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, aquaticanimal (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. The Effect of Fish Feeds Another often-overlooked facet of the aquaponic process or method is that all commercially-available, standard aquaculture feeds are formulated to meet the exacting nutrient requirements of fish and are not formulated to meet plant requirements. As a result, the correct mixture, ratios and concentrations of nutrients required for optimal plant growth and production are not present. Analysis of commercial fish feeds in the context of plant nutrient level and mixture requirements indicates an excess of nitrogen, medium to low levels of phosphorus, magnesium and sulfur and very low levels of calcium and potassium. The major plant-associated nutrient derived from commercial fish feeds is nitrogen because they contain a relatively high proportion of protein, which fish metabolize to produce amino acids to support growth and produce energy. Fish use some of the nitrogen in feed to build protein in their bodies but the majority is released as dissolved waste in the form of ammonia. Phosphorus contained in fish feed mostly ends up after fish metabolism as solid (fecal) waste. The nitrogen to phosphorus ratio in fish feed is critical to plants in an aquaponic system. Plants generally require an approximate N:P ratio in the range of 2:1 to 5:1. Feeds with high 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. (CONTINUED ON PAGE 22) FIGURE 2. The fish component (RAS) of the commercial aquaponic analogue built in New Zealand to compare the SymbioponicTM aquaponic method with standard hydroponics. An often-overlooked facet of the aquaponic process or method is that all commercially-available, standard aquaculture feeds are formulated to meet the exacting nutrient requirements of fish and are not formulated to meet plant requirements. As a result, the correct mixture, ratios and concentrations of nutrients required for optimal plant growth and production are not present.
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