Introduction
Aquaponics is increasingly recognized as a sustainable food production strategy that integrates aquaculture and hydroponics through internal nutrient recycling, reducing water use and dependence on synthetic fertilizers. This approach is particularly relevant in arid and semi-arid regions where freshwater scarcity and harsh climatic conditions constrain conventional agriculture. However, aquaponic productivity depends not only on system design but also on biological stability, especially the establishment of nitrifying microbial communities responsible for converting toxic ammonia into plant-available nitrate. During early operation, many systems experience instability characterized by pH decline, ammonia accumulation, and reduced fish and plant performance.
Floating raft and media-based systems are among the most common aquaponic configurations. Media-based systems may promote faster microbial colonization because of increased surface area, whereas floating systems are often simpler and easier to manage. Despite these differences, comparative evidence under hot arid conditions remains limited, especially using high-value marine or euryhaline fish species.
Asian seabass (Lates calcarifer) is an economically important species with tolerance to a wide salinity range, making it a strong candidate for aquaponics in coastal dry regions. Basil (Ocimum basilicum) and mint (Mentha sp.) are commercially attractive herbs commonly grown in aquaponics due to rapid growth and moderate nutrient demand.
This study compared floating and media-based aquaponic systems for integrated production of Asian seabass, basil, and mint under greenhouse conditions in Oman. We hypothesized that although system design may influence early-stage water quality dynamics, both systems would converge toward similar performance once nitrification processes were established.
Materials and Methods
The experiment was conducted over 115 days at the aquaponics research facility of Sultan Qaboos University. Six independent aquaponic units were used, each consisting of a fish tank (80 × 40 × 40 cm), sedimentation drum, and plant tank (80 × 40 × 20 cm). Three units were configured as floating raft systems and three as media-based systems using hydrostones.
Asian seabass with an initial mean weight of 163.05 ± 66.95 g were stocked at 7–8 fish per tank to equalize biomass. Fish were fed 2–3 times daily according to feeding response. Basil seedlings were initially planted (8 plants per tank), followed by mint seedlings (3 plants per tank) after basil harvest.
Fish weight and length were measured monthly. Plant height was monitored monthly. Water temperature, dissolved oxygen (DO), and pH were recorded weekly, while ammonia, nitrite, nitrate, phosphate, and silicate were analyzed monthly using standard seawater analytical methods. Differences between treatments were evaluated using independent sample t-tests.
Results
No significant differences were observed between floating and media-based systems for temperature, DO, overall pH, ammonia, nitrate, phosphate, silicate, fish growth, or plant growth.
However, transient instability occurred during Weeks 3–5, when the floating system exhibited significantly lower pH than the media-based system (p = 0.02). During the same period, reduced fish feeding activity and slower plant performance were observed.
Ammonia concentrations were highest during the first two to three months and declined thereafter, indicating progressive establishment of nitrification. Nitrite also decreased over time, while nitrate remained relatively stable in both systems.
Final fish weights were 275 g in floating systems and 281 g in media systems, with identical specific growth rates (1.8% day-1). Final fish lengths were approximately 27 cm in both treatments. Survival rates were 62.5% and 67.3% in floating and media systems, respectively.
Basil and mint showed comparable growth between systems, although slightly greater final plant height was recorded in floating units.
Discussion
The results indicate that system stability rather than physical design was the principal determinant of long-term aquaponic performance. Although media-based systems likely offered greater surface area for microbial attachment during start-up, both configurations converged toward similar water quality and biological outputs once nitrifying communities became established.
The early pH depression and elevated ammonia observed in the floating system are consistent with immature nitrification and insufficient buffering capacity. Nitrification releases hydrogen ions, which can lower pH and temporarily reduce feed intake, nutrient uptake, and fish welfare. Once microbial communities matured, nitrogen transformation improved and both systems achieved comparable functional performance.
Despite similar growth rates, survival remained moderate in both treatments. This suggests that fish survival is more sensitive than growth to short-term environmental stress, particularly fluctuations in pH, temperature, and early nitrogen accumulation. Abrupt seasonal cooling from 30°C to 20°C may also have weakened immunity and increased disease susceptibility.
From an applied perspective, both floating and media-based systems are suitable for aquaponic production in arid regions. However, success depends on rapid system maturation, effective biofiltration, and control of pH and temperature during the initial operational phase.
Conclusion
Both floating and media-based aquaponic systems successfully supported the co-production of Asian seabass, basil, and mint under greenhouse conditions in Oman. No major long-term performance differences were detected between system types. Instead, early-stage environmental instability and delayed nitrification had stronger effects on fish survival and short-term productivity than system configuration itself.
Acknowledgment
The authors thank Mr. Harib Al-Habsi and Mr. Badar Al-Buwaiqi for the laboratory analysis of nutrients.
Selected References
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