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In aquaponics, the aquaculture portion of the integration equation is broadly applied in a tank-based context, where the fish are kept in tanks, the water is filtered via mechanical (solids removal) and biological (ammonia transformation to nitrate) mechanisms and dissolved oxygen is maintained, either via aeration or direct oxygen injection (Rakocy et al. 2006; Lennard 2017).
As has been argued in Sect. 5.0 (Introduction) of this chapter, historical examples of chinampas (Somerville et al. 2014) and Asian rice paddy farming (Halwart and Gupta 2004) as early iterations of aquaponics are unfounded and inappropriate examples of aquaponic principles, because modern aquaponics relies on designed additions of fish and fish feeds to supply a designed level of nutrition to the plants, and therefore, these historical examples cannot be considered in any way similar (Lennard 2017).
The above historical examples, which rely on soil-based plant culturing systems, lead to the question of what aquaculture technologies are suitable for aquaponic integration. Soil-based, extensive, freshwater pond aquaculture of fin fish is the largest culturing method applied to produce freshwater fish for human consumption (Boyd and Tucker 2012). A pond approach relies on the earthen base of the pond, and the associated microflora present in that soil, to treat and remediate the wastes produced from fish culture so the fish are not living in water that has a potential to be toxic to them (Boyd and Tucker 2012). Because this system relies on the inherent treatment capacity of the earthen pond itself, fish densities are relatively low compared to other aquaculture methods. Because the fish densities are low (and therefore the associated feeding rates are low) and the pond itself treats and uptakes the waste nutrients produced by the fish, pond waters exhibit extremely low water nutrient concentrations. These pond system aquatic nutrient concentrations are so low that they are often inappropriate as nutrient sources for substantial, commercial aquatic plant production methods (Lennard 2017). Therefore, ponds are not an appropriate aquaculture method to be integrated with hydroponics in terms of acceptable plant production rates.
Similarly, raceway fin fish culture methods (as regularly applied for freshwater Salmonid production), which supply very large volumes of water at high turnover rates, or low residence times, through controlled raceway fish culture tanks, are not appropriate for aquaponic integration because the high water turnover rates do not allow adequate nutrient accumulations to meet plant nutrient requirements (Rakocy and Hargreaves 1993).
The most appropriate fish culture technologies to apply within an aquaponic integration context are those that culture fish in tanks and allow a level of fish waste accumulation (plant nutrient accumulation) that has the potential to lead to water nutrient concentrations that are applicable for efficient hydroponic plant production (Rakocy et al. 2006). Recirculating Aquaculture System (RAS) principles are broadly applied to aquaponics because they provide the methodologies to successfully keep and grow the fish, in controlled volumes of water, with low daily water replacement rates, that allow fish waste (plant nutrient) accumulations that approach those required to efficiently hydroponically culture the plants (Rakocy and Hargreaves 1993; Lennard 2017). The complexities and design requirements of RAS are discussed in Chap. 3 of this book. Suffice to say that RAS fish culture is the only real appropriate method to apply for fish culturing components in an aquaponic context and as discussed above, soil-based aquaculture systems, such as extensive pond systems and raceway culture systems, cannot provide the nutrient requirements of the plants and therefore should not be considered.