WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2025 41 (CONTINUED ON PAGE 42) as noted, of control of water and can be used in a decoupled or split aquaponics system, where water from the fish is conditioned before being applied to plants. This allows optimization of pH (likely reducing pH for the plants); mixing of salt and fresh water if available and appropriate; addition of needed plant nutrients such as iron or other nutrients, and optimization of nitrogen (e.g. maximizing nitrate, generally preferred by plants). Open Impoundment Challenges and Opportunities Shrimp and other species may be grown in impoundments near the coast. These impoundments, in theory, are somewhat ‘closed’ and may therefore be appropriate for some aquaponics principles, possibly growing salt tolerant or salt loving plants (halophytes). However, as noted previously, it may be preferred that there be a separate impoundment that can help treat the wastewater before discharging to reduce nutrients. One approach would be to use halophytes such as Salicornia or sea beans. This is an edible species that can grow in 10-30 ppt. They are used fresh as a slightly salty, nutrient rich vegetable or garnish; and can be dried to produce ‘green salt,’ a natural, lower salt, high nutrient salt substitute (Figure 5). Some species of duckweed (Lemna) have been found to tolerate moderate salinities up to about 10 ppt, and may also provide animal feeds — some species are high in protein. They are highly effective at uptaking both nitrogen products (nitrites, nitrates); as well as phosphorus, thus minimizing eutrophication concerns. Raceway and Open Water Challenges and Opportunities Raceway systems imply flow through, which often means that outflowing water has higher nutrients. In cage systems and other open marine systems, nutrients may be released directly to the environment. In these cases, it may be difficult to address these excess nutrients, but multitrophic approaches including algae FIGURE 4. Left) Strawberries grown in intermittent salinities (up to 4.5 ppt), and Right) ‘rinsed’ with fresh irrigation water showed acceptable growth and produced sweeter berries (C. Pascual). Shrimp and other species may be grown in impoundments near the coast. These impoundments, in theory, are somewhat ‘closed’ and may therefore be appropriate for some aquaponics principles, possibly growing salt tolerant or salt loving plants (halophytes). However, as noted previously, it may be preferred that there be a separate impoundment that can help treat the wastewater before discharging to reduce nutrients.
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