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

Background Aquaponics is increasingly promoted as a sustainable food production system, yet the production scale required for economic viability remains poorly understood, particularly in resource-constrained contexts. Methods This study developed a techno-economic scale-up framework using empirical data from a low-tech pilot combining Nile tilapia ( Oreochromis niloticus ) and tomato ( Solanum lycopersicum ) in Bandundu, Democratic Republic of the Congo. The reference system (0.2 m 3 fish-rearing volume and 1 m 2 cultivation area) was projected across scale factors k = 1–50. A managerial-efficiency coefficient ( ε = 0–0.25) was incorporated to represent potential efficiency gains with increasing scale. Economic performance was evaluated under baseline and favorable scenarios using annual operating cash flow (CF) and net present value (NPV). Results Under baseline conditions, no simulated scale achieved positive CF or NPV. Under the favorable scenario, the operating cash flow threshold (CF = 0) occurred at k = 4.37, corresponding to a fish-rearing volume of 0.87 m 3 and a cultivation area of 4.37 m 2 . The financial viability threshold (NPV = 0) occurred at k = 34.21, equivalent to 6.84 m 3 and 34.21 m 2 , respectively. With favorable economic assumptions but no scale-dependent efficiency gains ( ε = 0), neither threshold was reached. Sensitivity analysis showed that the modeled financial threshold depended strongly on labor cost, tilapia price, tomato productivity, investment scaling, discount rate, and the assumed scale-dependent efficiency trajectory. Marginal analysis under the favorable scenario showed positive incremental operating returns at all scale transitions, with the marginal benefit–cost ratio increasing from approximately 1.02 to 1.23. Discussion These findings indicate that economically viable expansion depends not on physical scale alone, but also on biological performance, cost efficiency, market value, and operational management.