34 MARCH 2023 • WORLD AQUACULTURE • WWW.WAS.ORG work cooperatively with aquaponic farmers to ensure on-farm results are consistent with reported research. Economic viability for the small farmer should be the priority of research. System design can play a key role in efficiency and related profitability of an aquaponic farm. For example, temperate producers may consider using a decoupled aquaponic system that separates fish and plant production for optimized energy, heating and water quality control. Separating the systems allows a farmer to shut down a portion of their operation when utility costs get too high to break even. Only 16 percent of surveyed producers operate decoupled systems, indicating a complexity and unfamiliarity with alternate system designs. Coupled, or single loop, systems are by far more common, largely due to the available design schematics and years of production data from the University of the Virgin Islands. Although most farms in the survey were under the 1000-m2 profitability threshold, understanding local regulations on energy buy-back programs from solar or a gas-based combined heat and power unit may be the tipping point that brings a farm from loss to profit. A cold-weather adaptation for aquaponics is indoor or warehouse farming in well-insulated buildings where the growing environment can be easily regulated (Eaves and Eaves 2018). Aquaponic producers operating indoors have flexibility to design systems that maximize space and heat efficiency. Vertical production systems use shallow trays on racks with three to five layers and grow lights directly above the crops (Avgoustaki and Xydis 2020, Eaves and Eaves 2018). These ‘plant factories’ produce more plant biomass per unit area than greenhouses and consume only 2 percent of the water of a similar size field operation by condensing and reusing moisture in the air (Avgoustaki and Xydis 2020). Some farms use on-site generators that create electricity, heat and CO2 for plant uptake in a costeffective way (Baganz et al. 2020). Urban growers can also take advantage of off-peak power to maximize profit (Avgoustaki and Xydis 2020). The ultimate profitability of these operations remains to be seen, but they certainly look attractive. Challenge 2: Operations and Management Production. Surveyed producers most often grew tilapia, ornamental fish and catfish, combined with lettuce, leafy greens, basil and tomato. Selling fish on a small scale is a clear bottleneck. Processing fish pushes retail prices beyond the consumers’ willingness to pay, while live direct sales from farms is sporadic and limited to specific clientele. Plant production dominates in aquaponic systems. The rule-of-thumb that ¾ of all revenue comes from plants appears reasonably accurate. Daily operational tasks such as balancing fish and plants, sourcing/ availability of inputs, resource management (energy, electricity, etc.) and finding reliable labor are key challenges identified by producers (Pattillo et al. 2022a). Producers with more than five years of experience reported these challenges more often than those with less experience (Pattillo et al. 2022a). Aquaponics takes time and effort to master, particularly for low-tech systems without automation (Kyaw 2017). Seasoned operators find that careful management of energy, labor, water, plant and fish inputs are necessary for efficient production and minimized costs (Quagrainie et al. 2017, Silva et al. 2019). Reducing resource expenditures required to grow a crop is one of the most attractive aspects of aquaponics, particularly water and nutrient usage. However, the climate of the growing location heavily influences production (Goddek and Kröer 2019). Love et al. (2015) reported a 5:1 ratio by weight of leafy greens to feed input to the system under optimal conditions. However, over a full production year 1 kg of crops requires 104 L of water, 0.5 kg of feed and 56 kWh of energy on average, making the plant to feed ratio closer to 2:1. Environmental control is a major cost constraint of growing in a temperate environment. Locations with more stable environments and low seasonal variation in temperature tend to be more energy and nutrient efficient (Goddek and Kröer 2019). Love et al. (2015) reported an average monthly energy cost in Maryland of $6/kg of plants produced, ranging from $1/kg in the summer to as high as $55/kg in January. The energy cost for lettuce production in Hawaii is $0.73/kg (Tokunga et al. 2015). Labor. Finding reliable workers is a common challenge for aquaponic producers given the multitude of skills required for
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