Introduction
Haloponics can be defined as aquaponic systems operating with brackish water at salinity levels ranging from 1 to 35 [g/L], while Maraponics indicates systems operating with seawater, e.g. salinity at or above [g/L]. Compared with freshwater aquaponics, these systems can operate in arid coastal areas and are resilient to climate change related water shortage. Furthermore, marine fish species which can be farmed in both haloponics and maraponics systems, such as seabass and seabream, have, in general, a higher market value, compared with those farmed in freshwater aquaponics, e.g. common carp, tilapia. On the other hand, the use of saline water restricts the range of plant species which can be co-produced. The economic sustainability of aquaponic systems is often questioned, due to their high energy demand: this issue is even more relevant for attracting investors in new integrated agrifood systems, such as haloponics and maraponics. In this paper we present the results of a case study, in which two classical methodologies were used for assessing the economic sustainability of coproducing seabream (Sparus aurata) and marsh samphire (Salicornia Europea), a halophyte tolerant to high salinities and commonly found in Mediterranean coastal areas. This combination seems promising, given the increasing interest in samphyre as food and nutraceuticals.
Materials and methods
Seabream and samphire were co-coproduced in a pilot plant located at Ca' Foscari University premises from April 2024 to August 2025. Seabream juveniles were stocked in April 2024, average weight 40 grams, and harvested in August 2025. Samphyre seedlings were stocked in April 2024: plants were tagged and repeatedly pruned, until November. Pruned biomass was weighted and added to the harvested one to obtain an estimate of the total biomass production per plant. Seedling were restocked in April 2025: individual plant biomass was estimated on a weekly basis by extracting each plant and relocating it after weighting. Seabream were farmed at a low density, about 10 kg/m3, and weighted individually every month. The plant was equipped with automatic sensors for determining water temperature, salinity, dissolved oxygen and pH downstream the fish tanks and the greenhouse every 15 minutes. Alkalinity, Total Ammonia Nitrogen (TAN), Nitrate and Reactive Phosphorus were monitored on a weekly basis. The data were used to identify and validate the Knowledge Base Model (KBM) component of a Digital Twin prototype of an aquaponic plant. The model formulation and the results are presented in detail in the deliverables available at the BeBlue Italy-Slovenia INTERREG project website: https://www.ita-slo.eu/it/beblue. The KBM was used to upscale the production and to design a virtual haloponics plant, partitioned into production lines of the capacity of 2000 tonnes/year of seabream each. The virtual plant was used as a reference model to estimate total capital investments and annual operating costs for the transition to an industrial scale. Revenues were estimated based on a price of ���8/kg for sea bream and ���10/kg for samphyre, based on an analysis of current wholesale market prices in Italy. Based on these data, several economic sustainability indicators were calculated. In the first phase, a cost/benefit analysis was performed by discounting the annual cash flow values ������for the considered 10-year plant lifetime. The set of indicators included: net present value (NPV), internal rate of return (IRR), and payback period (PBT). In a second phase, a forecasted income statement was developed to determine a company's profit and return on investment (ROI).
Results and discussion
The results are summarized in Table 1, which presents the estimated biomass yields of a 2000 tonne seabream production line, and Table 2, which shows Capital Expenditure (CaPex), Operational Expenditure (OpEx), revenues and the economic indicators. The surface of the Green House, see Table 1, was estimated assuming a Nitrogen Use Efficiency of 70%. Based on the results of the pilot, we assumed that the samphire seedling would take 2 months to reach an average weight of 300 grams, using LED lights, giving five crops per year.
Table 1. Estimated biomass yield of a 2000 seabream production line.
Seabream
Samphyre
Maximum stocking density [kg/m3]
25
Plant density [N plant/m2]
50
Time to harvest [year]
1
Time to harvest [year]
0.17
Initial individual weight [g]
20
Initial individual weight [g]
2
Individual weigth at harvest [g]
400
Individual weigth at harvest [g]
300
Mortality [%/year]
10
Mortality [%/cycle]
5
Total tank volume [m3]
80
Commercialized fraction [%]
60
Feed Conversion Ratio
1.3
Nitrogen Use Efficiency [%]
70
Total biomass production [kg/year]
1900
Total available Nitrogen [kg/year]
100
Total excreted Nitrogen [kg/year]
143
Total commercial biomass
20900
Green House surface [m2]
465
Table 2. Revenue, CaPex, OpEx and economic sustainability indicators for a company producing 2000 tonnes seabream/year and about 20,000 tonnes samphire/year.
CaPex
Opex
Economic indicators
RAS [Euro]
148,650
Personnel [Euro/year]
64,350
Profit [Euro/year]
47.016
GreenHouse [Euro]
120,093
Feed [Euro/year]
4,199
NPV [Euro]
209.140
Machinery [Euro]
75,000
Electricity [Euro/year]
42,562
IRR [%]
16.9
Total [Euro]
343,743
Other costs
24,589
PBT [year]
5
Total [Euro/year]
135,700
ROI [%]
23%
Revenue seabream
16,000
Revenue samphyre
200,000
Total revenue
216,000
The results presented in Table 2 suggest that a 10-year long investment project in seabream-samphyre haloponics is viable and could produce interesting economic ouputs. All indicators are positive: compared with investments in other agrifood systems a PBT of five years is fully acceptable. As haloponics is still at an early development stage, there is also large margin for samphire seedling selection and optimization the energy use, which may lead to further reduction of both CaPex and OpEx. However, the market positioning of both fish and vegetable products is crucial for the absorption of the total production quantity, as well as the selling price: the situation to be assessed is significantly different if the final recipients are, for example, large-scale retail trades of the final consumer.
Acknowledgement
This research was co-funded by the INTERREG Project "BeBlue" https://www.ita-slo.eu/it/beblue and the iNEST project, https://www.consorzioinest.it/, Spoke 7.
References
Verma A.K., M.H. Chandrakant, V. C. John, R. M. Peter, I. E. l John. Aquaponics as an integrated agri-aquaculture system (IAAS): Emerging trends and future prospects. Technological Forecasting & Social Change 194 (2023) 122709