Aquaponics, the pairing of fish farming with soilless plant cultivation in a single recirculating water loop, is often promoted as a sustainable answer to food production in places where land and water are scarce. But a new modeling study from the Democratic Republic of the Congo suggests that the road from a backyard pilot unit to a financially sound enterprise is far longer and more conditional than most enthusiasts assume. Under realistic local prices, no simulated expansion of a low-tech tilapia and tomato system ever turned a profit, and even under generous economic assumptions the investment only paid for itself once the system had grown to roughly thirty-four times its original size.

The study, published in Frontiers in Sustainable Food Systems on 29 October 2026, was led by Jude Kifufu of the Baptist University of Congo, the University of Bandundu, and the University of Kinshasa, together with colleagues Gaétan Kalala, Patrick Mafwila, and Honoré Kiatoko. Rather than testing a large commercial farm directly, the team built what they call a techno-economic scale-up framework: a model that starts from hard empirical data gathered on a small working system in Bandundu, Kwilu Province, and then projects how costs, production, and revenues would evolve as the physical footprint grows.

The reference system was genuinely small. It consisted of a 0.2 cubic meter fish-rearing tank holding Nile tilapia, a single square meter of gravel-filled grow bed planted with tomato, a 50-liter swirl filter, a sump, a recirculation pump, and an aeration system. The unit ran outdoors from 6 April to 3 October 2024, a 180-day period covering one full tilapia cycle and two successive 90-day tomato cycles. Water temperature, pH, dissolved oxygen, and total ammonia nitrogen were monitored throughout, and biological parameters were averaged across three identical experimental units operated simultaneously. The fish grew from an initial mean weight of about 80 grams to roughly 282 grams, with survival of 92 percent and an apparent feed conversion ratio of 1.21.

The economics of that pilot unit were sobering on their own. Building it required an initial investment of USD 225.89, and its total annual cash operating cost came to USD 126.70, with electricity as the largest single item at USD 38.60 per year, followed by labor at USD 35.72 and feed at USD 19.44. Annual production totaled 12.98 kilograms of tilapia and 21.36 kilograms of tomato. Priced at the USD 5.00 per kilogram for tilapia and USD 1.50 per kilogram for tomato observed at three sales points in Bandundu’s central market, the system generated just USD 96.94 in annual revenue, leaving an operating deficit of USD 29.76 per year.

To explore what happens when such a unit grows, the researchers defined a scale factor k ranging from 1 to 50, where k multiplies both the fish-rearing volume and the cultivation area. Crucially, they did not assume that everything scales proportionally. Investment costs were modeled with a power-law relationship using an exponent of 0.65, reflecting sublinear growth of capital requirements, while operating costs were split into categories: feed, juveniles, seedlings, and transportation scaled with production, whereas electricity, water, labor, and maintenance scaled with physical size. A managerial-efficiency coefficient, rising from zero at the pilot scale to a maximum of 0.25 at fifty-fold expansion, was applied to production-linked costs and outputs to represent potential gains in planning, labor organization, and task specialization as operations grow.

The results draw a sharp line between two kinds of financial failure. Under the baseline scenario, which used the pilot’s actual biological performance and observed Bandundu market prices, no simulated scale from k = 1 to k = 50 achieved positive annual operating cash flow or a positive net present value over a ten-year horizon at a 10 percent discount rate. At fifty-fold expansion, revenue reached USD 6,058.75 per year, but cash operating expenditure climbed to USD 6,881.25, leaving an annual deficit of USD 822.50. Net present value stayed negative throughout, ranging from minus USD 408.72 at the pilot scale to minus USD 7,926.19 at k = 50. Physical expansion alone, in other words, never overcame the unfavorable relationship between what the system earned and what it cost to run.

The picture changed only under a deliberately favorable scenario that combined a 20 percent higher tilapia price of USD 6.00 per kilogram, a 20 percent reduction in feed cost, a 30 percent reduction in electricity cost, and the assumed scale-dependent efficiency gains. Under those conditions, the operating cash flow threshold, the point at which annual revenue first covers recurring cash expenditure, occurred at k = 4.37, equivalent to 0.87 cubic meters of fish-rearing volume and 4.37 square meters of cultivation area. But profitability at the operating level was still not enough. The financial viability threshold, where net present value finally crossed zero, was not reached until k = 34.21, corresponding to 6.84 cubic meters and 34.21 square meters. The first integer scale at which the investment became viable was k = 35, with a net present value of about USD 77.70, an internal rate of return of roughly 10.8 percent, and a payback period of 5.94 years.

That wide gap between the two thresholds is the study’s central conceptual contribution. A system can cover its running costs year after year and still fail to justify the capital sunk into it once the time value of money is accounted for. The authors show this vividly with a control scenario that kept all the favorable price and cost assumptions but removed the scale-related efficiency gains entirely. In that case, neither threshold was ever reached: operating cash flow remained negative at every scale, standing at minus USD 65.60 per year even at fifty-fold expansion, and net present value never came close to zero. The positive transitions observed in the main favorable model therefore depended not on size itself but on the assumed improvements in operational performance that come with it.

Sensitivity analysis underscored how fragile those thresholds are. A 30 percent reduction in labor cost lowered the financial viability threshold to k = 14.40, while a 30 percent increase prevented viability anywhere within the modeled range. A 10 percent rise in the tilapia price cut the threshold to k = 17.82, whereas a 10 percent fall eliminated it. A 20 percent increase in tomato productivity lowered the threshold to k = 20.23, while a 20 percent decrease prevented viability. The investment scaling exponent, the discount rate, fish survival, and the feed conversion ratio all shifted the frontier as well: a 10 percent improvement in feed efficiency lowered the threshold to k = 30.38, and raising the maximum efficiency coefficient from 0.25 to 0.30 moved it down to k = 29.77. Marginal analysis added a further layer, showing that under baseline conditions the marginal benefit-cost ratio stayed below 1 at every scale transition, from 0.79 to 0.96, meaning each expansion step added more cost than revenue. Under the favorable scenario, that ratio rose from about 1.02 to 1.23, indicating progressively stronger incremental operating returns, though the authors stress that this measure excludes capital investment and the time value of money.

The authors are careful about what their model can and cannot claim. The efficiency coefficient and the investment exponent are scenario assumptions, not constants estimated from farms operating at multiple scales, and the biological inputs come from three small pilot units that may not capture the variability of commercial production. The thresholds are model-derived boundaries specific to the Bandundu reference system, not universal recommendations to build a facility thirty-four times larger than a pilot. Still, for resource-constrained settings where unreliable electricity, limited finance, and high transport costs complicate aquaponic expansion, the practical message is clear: improving fish survival, feed efficiency, crop productivity, labor organization, and market access should come before major capital spending, because scale by itself solves nothing.

Subject of Research: Techno-economic modeling of scale-up thresholds for a low-tech tilapia and tomato aquaponic system in the Democratic Republic of the Congo

Article Title: Economic viability thresholds for aquaponic systems: a scale-up modeling framework based on empirical data

Article References: Kifufu, J., Kalala, G., Mafwila, P., & Kiatoko, H. (2026). Economic viability thresholds for aquaponic systems: a scale-up modeling framework based on empirical data. Frontiers in Sustainable Food Systems, 10, Article 1866776. https://doi.org/10.3389/fsufs.2026.1866776

Image Credits: AI Generated

DOI: 10.3389/fsufs.2026.1866776

Keywords: aquaponics, Nile tilapia, tomato, techno-economic modeling, scale-up, net present value, cash flow threshold, sensitivity analysis, Democratic Republic of the Congo, financial viability, marginal analysis, sustainable food systems