Towards circular aquaponics in small-scale rural farms

Small-scale aquaculture is a pillar for food security and economic development for millions of people, especially in the Global South. However, it faces challenges such as dependence on external inputs and waste management. A recent study published in the journal Resources explores how integrated circular aquaponics (ICAq) can transform these challenges into opportunities, creating more sustainable and self-sufficient systems.

The concept of ICAq is defined as: “an aquaponics or aquaponic agriculture system with additional modules that leverage material flows to increase the system’s sustainability by improving internal circularity.” This approach not only recycles water and dissolved nutrients but also converts system byproducts, such as fish sludge and plant residues, into valuable inputs like fertilizers, bioenergy, and even ingredients for fish feed.

How does an integrated circular aquaponics system work?

Researchers from the Center for Research in Food and Development, the National Autonomous University of Mexico, the Leibniz Institute of Freshwater Ecology and Inland Fisheries, and São Paulo State University (Unesp) proposed a methodology to identify and analyze circular processes that can be implemented in small-scale rural aquaculture farms. The study focused on low-tech and easily adaptable solutions, considering the investment and technical training limitations common in these contexts.

The analysis identified several key pathways to “close the loop” within an aquaponic farm:

• Solid waste treatment: Aquaculture sludge, fish processing residues, and agricultural waste, traditionally a problem, are converted into a source of resources.
• Input generation: Through processes like composting, vermicomposting, anaerobic digestion, and ensiling, this waste is transformed into fertilizers, substrates for seedlings, and even bioenergy.
• Feed production: One of the most innovative proposals is the use of waste to cultivate insects, such as the black soldier fly (Hermetia illucens), whose meal can replace part of the fishmeal in aquaculture diets, reducing costs and external dependence.

Transforming waste into valuable resources

The study highlights several technologies and processes with great potential for rural aquaculture.

Organic fertilizers and substrates from waste

Composting and vermicomposting of aquaculture sludge (AS) and agricultural waste (AW) are low-cost methods for producing nutrient-rich fertilizers. The combination of AS (rich in nitrogen) with AW (rich in carbon) allows for the ideal C:N ratio for efficient composting. This compost can be used as a substrate for the system’s own seedlings, closing the nutrient loop. Ensiling, another simple process, transforms fish waste into a liquid fertilizer or a highly digestible feed ingredient.

Bioenergy and nutrients from digestion

Anaerobic digestion (AnD) of waste not only produces biogas, which can be used as an energy source on the farm, but also a liquid effluent (centrate) rich in nutrients like ammonium, phosphorus, and potassium, which can be reused in the system. Although the direct application of this concentrate in hydroponics has shown variable results, it has proven ideal for cultivating microalgae or duckweed, which can in turn become ingredients for fish feed. Aerobic digestion (AD), on the other hand, produces a nitrate-rich centrate, which is more directly assimilable by the plants in the hydroponic component. Recent research shows that integrating an aerobic digestion reactor can improve the concentrations of key nutrients in the water and the performance of both fish and plants.

Towards self-sufficiency in fish feed

The cost of feed is one of the largest expenses in aquaculture. ICAq offers alternatives to produce ingredients on the farm itself:

• Insect meal: Cultivating black soldier fly larvae on aquaculture and agricultural waste is a promising strategy. These larvae are rich in protein, and their meal has been shown to replace up to 75% of fishmeal in diets for the African catfish (Clarias gariepinus) in aquaponic systems, with no negative effects.
• Aquatic macrophytes: Plants like duckweed (Lemna spp.) or water spinach (Ipomoea aquatica) can be grown within the same system and used as a protein supplement in fish diets.
• Fermented ingredients: Fermenting plant-based ingredients or fish silage can improve their digestibility and nutritional value, eliminating anti-nutritional compounds and providing probiotic benefits.

Medicinal plants for fish welfare

Finally, the study suggests cultivating plants with phytotherapeutic properties within the aquaponic system. Herbs such as basil, rosemary, or oregano have demonstrated antibacterial, immunostimulant, and anti-stress effects in fish. Aquaponics could even enhance the concentration of these bioactive compounds in the plants.

Conclusions and implications for the future

The implementation of integrated circular aquaponics (ICAq) on small-scale rural farms has the potential to improve the environmental sustainability and economic viability of aquaculture. By transforming waste into valuable inputs, producers can reduce costs, diversify their income, and decrease their environmental impact.

However, the authors emphasize the need for more research to quantify the material and energy flows in these systems, evaluate the technical and economic feasibility of each process in specific contexts, and develop circularity indicators adapted to ICAq.

This approach is not a one-size-fits-all solution but a framework that must be adapted to local conditions, leveraging traditional ecological knowledge and community participation to design truly resilient and sustainable systems.

Reference (open access)
Silva, L., Martinez-Cordero, F. J., Baganz, G., Baganz, D., Hernández-Pérez, A., Coronado, E., & Portella, M. C. (2025). Advancing Circularity in Small-Scale Rural Aquaponics: Potential Routes and Research Needs. Resources, 14(8), 119. https://doi.org/10.3390/resources14080119

Milthon Lujan

Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.