Assessment of aquaponics as a sustainable food production system for urban agriculture

Introduction

Aquaponics combines recirculating aquaculture and hydroponics into a single loop where fish waste provides nutrients for plants, and plants filter water returned to fish tanks [1,2] . Its application to urban food production has gained relevance as cities in Latin America face rising food prices and limited arable land [3] . Brazil's urban population exceeds 87%, and over 19 million Brazilians live in food-insecure households [4] . Aquaponics produces food vertically and recirculates 90-95% of its water, making it suited to space-and water-constrained urban settings [5,6] . Previous research focused mainly on temperate greenhouse environments [7] , with limited data from tropical semi-covered systems affordable for community adoption in Brazil [8] . This research assessed aquaponics against hydroponics and soil-based production over a full year, measuring crop yields, fish production, water use, and financial returns under Brazilian conditions.

Experimental system design

Three production systems were established under a semi-covered structure (50% shade cloth) at the ESALQ campus, University of São Paulo, Piracicaba (22.7129°S, 47.6279°W). The aquaponics unit consisted of two 1,000 L fish tanks connected to four media-bed grow beds (1.2 × 1.0 × 0.3 m each, expanded clay aggregate). The hydroponics unit used NFT channels of equivalent growing area. Soil-based plots occupied the same footprint in raised beds with local Oxisol. Each system was replicated three times. Water was recirculated by 40W submersible pumps in aquaponics and hydroponics. Nile tilapia fingerlings were stocked at 20 fish/m³.

Material and Methods

Material

Lettuce (Lactuca sativa cv. Vanda) and basil (Ocimum basilicum cv. Genovese) seedlings were transplanted at 21 days after sowing. Nile tilapia (Oreochromis niloticus) fingerlings (mean weight 12.4 g) were obtained from the ESALQ fish hatchery. Commercial fish feed (32% crude protein, Guabi Nutrição Animal) was provided at 3% body weight daily. Expanded clay aggregate (8-16 mm, Cinexpan) served as the biofilter medium. Hydroponic nutrient solution followed the Furlani formulation [9] .

Methods:

The trial ran from March 2022 to February 2023, approved by the ESALQ Ethics Committee on Animal Use (Protocol CEUA-ESALQ 2022/03). Lettuce was harvested every 35-40 days (8 cycles) and basil every 28-32 days (10 cycles). Fish were harvested at month 6 and month 12 when they reached market size (~500 g). Water quality pH, dissolved oxygen, ammonia, nitrite, nitrate, and temperature was measured weekly. Water consumption was tracked by logging all additions to each system. Nutrient recovery efficiency was calculated as the proportion of nitrogen in fish feed recovered in plant and fish biomass [10] . Crop yields were recorded as fresh weight per square meter. Economic analysis included all capital and operational costs with revenue from produce and fish sales at Piracicaba wholesale market prices. Data were analyzed using ANOVA and Tukey's test (p<0.05) in R v4.2.2.

Seasonal performance

Ambient temperatures ranged from 16.8°C (July) to 34.2°C (January). Fish growth slowed during the cooler months (June-August), with feed conversion ratios rising from 1.34 to 1.78. Lettuce production peaked in the mild dry season (April-August) when temperatures favored vegetative growth without bolting. During the hot wet season (November-February), basil outperformed lettuce, producing 18% higher yields than its coolseason average. Water consumption across all systems was highest in October-January due to elevated evapotranspiration. Despite higher setup costs, aquaponics generated the largest net annual return (BRL 2,436) thanks to the dual revenue stream from produce and fish (Table 2). The system reached break-even at month 9, compared to month 7 for hydroponics and month 11 for soil cultivation. Water quality distributions (Figure 1) show that aquaponics maintained adequate dissolved oxygen while keeping nitrates far below hydroponic levels. The production comparison (Figure 2) highlights the additional tilapia output and superior nutrient recovery of the aquaponics system.

Results

Cost analysis:

The main cost advantage over hydroponics was eliminating commercial nutrient solutions (BRL 1,240/year saved), replaced by fish feed (BRL 864/year). Fish revenue (BRL 1,392/year) was the decisive economic differentiator. For community adoption, a cooperative of five households sharing one system could reduce per-household setup costs to BRL 964.

Discussion: The 78.2% water savings over soil-based production confirm earlier estimates. Goddek et al. [2] reported 80-90% water reduction in closed aquaponics under greenhouse conditions. Our slightly lower figure reflects the semi-open tropical setup with higher evaporative losses. The 22.1% advantage over hydroponics reflects biological filtration in media beds reducing the need for periodic nutrient solution replacement [11] . Lettuce yields of 4.83 kg/m² fell 5.7% below hydroponics, consistent with Rakocy et al. [12] who noted a 4-10% yield gap for leafy vegetables, likely from suboptimal nutrient ratios in fish waste [13] . But the aquaponics yield was 47.7% above soil production, and tilapia (18.7 kg/m³) added protein absent from other systems. The 14.3% profit margin and 9-month payback align with Love et al. [14] who surveyed commercial operations finding 8-18% average margins.

Conclusions: Aquaponics performed well as an urban food production system under Brazilian tropical conditions. Combined output of vegetables and fish made it the most productive and profitable system overall. Water efficiency was the best of all three methods an important advantage for waterstressed cities. The dual revenue stream justified higher initial costs. For Brazilian cities seeking to expand local food production, aquaponics represents a practical option that merits support through training and community investment, providing fresh produce and protein while using a fraction of conventional water requirements.

References

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