WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2025 39 Aquaponics is the culture of aquatic animals (e.g. aquaculture) and the use of the nutrients in the waste water as a medium for hydroponic plant growth, hence aqua-ponics. Common systems use fresh water with hardy fish species (e.g. tilapia) and quick growing plant species such as lettuce and basil. Small scale systems are common and there are some larger commercial systems. Aquaponics has some challenges of its own: fish generally require a slightly higher pH (often 7-8), while plants may prefer more acidic conditions (6-7). One response to this challenge is to separate the fish and plant components, allowing the manipulation of water quality to optimize for each species. One could also argue that land application of aquaculture wastes is a primitive form of aquaponics, and works well as supplemental irrigation water and nutrients for the plants. But remember, this is fresh water, whereas salt water adds further challenges. Marine aquaculture refers to water that is salty or brackish. Marine aquaculture may include Recirculating Aquaculture Systems (RAS), Open Water Systems, Impoundments and Raceways, focusing on growing aquacultural products, often finfish or crustaceans in salty or brackish water. As noted, applying salty water may kill most plants. However, marine aquaculture is growing because, while fresh water is limited in many locations, growing fish, crustaceans, molluscs or other species can be done in a variety of salinities. In some cases these are open cage systems, where food that is not eaten may be lost or may add nutrients in the area with possible eutrophication. Other systems are closed (such as impoundments and RAS systems) and hence managing nutrients may be easier. Marine aquaponics refers to using salty, nutrient laden water to grow salt tolerant or salt loving plants. While there are challenges, there are also opportunities. The vast majority of water on our planet is in the oceans, so using this water to culture fish and plants can be effective. There is limited competition for the water, as opposed to the multiple needs for freshwater on land — for drinking water and agriculture. Therefore, using marine water to both culture fish and grow additional plant species could be a win-win if done effectively (Figure 1). Most coastal countries have substantial areas for marine aquaculture and aquaponics, while some inland countries have challenges with salinization of land where similar principles may be applied. Marine Recirculating/ RAS Challenges and Opportunities Recirculating systems generally use settling and/or filtration to remove solids and may have biofilters to convert AQUACULTURAL ENGINEERING SOCIETY CONTRIBUTED ARTICLE: Marine Aquaponics: Challenges and Opportunities Steven G. Hall and Christopher Pascual FIGURE 1. Top) Fish and plants can be harvested from marine aquaponics systems. Bottom) The system shown was used to scientifically assess response of plants to various salinities (see Pascual et al., 2024, Pascual 2025; S. Hall photos). (CONTINUED ON PAGE 40)
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