The global demand for sustainable food production has led researchers to explore innovative approaches that minimize environmental impact and maximize yield. One such promising approach is the integration of euryhaline fish and Mediterranean halophytes in aquaponics systems.
In a study published by researchers from the University of Thessaly, University of Patras, and Aristotle University of Thessaloniki, the impact of fasting and refeeding on the growth performance of seabass (Dicentrarchus labrax) and Baltic shrimp (Palaemon adspersus) was evaluated in a brackish water aquaponics system co-cultivated with Salicornia europaea. The study investigates whether compensatory growth in fish affects the performance of Salicornia in an aquaponics system.
Brackish Water Aquaponics
In aquaponics using brackish water, halophytes (such as Salicornia and sea fennel) play a vital role, along with euryhaline fish species native to the Mediterranean, like gilthead seabream and seabass. These species can adapt to a wide range of salinities, allowing for the cultivation of a greater number of plants that would otherwise be limited. Salt-tolerant halophytes, such as Salicornia, are promising candidates for saltwater aquaponics.
Mediterranean Species: A Perfect Match
Mediterranean euryhaline fish species, such as seabass and gilthead seabream, are well-suited for aquaponics systems due to their adaptability to varying salinity levels. These fish can thrive in brackish water environments, making them ideal candidates for marine aquaponics.
The Baltic Shrimp (Palaemon adspersus)
The Baltic shrimp, a species widely distributed in protected brackish waters, is a promising candidate for aquaculture. It is found in bays, lagoons, and estuaries of the eastern Atlantic, the Baltic, the Mediterranean, the Black Sea, the Caspian Sea, and the Aral Sea, as well as in the Atlantic area of Canada. Baltic shrimp are used as live feed in aquaculture, although they are predominantly employed as live bait for commercial, artisanal, and sport fishing.
Halophytes: Naturally Salt-Tolerant Plants
Halophytes, plants that can tolerate high salt concentrations, play a crucial role in aquaponics. Salicornia, a succulent halophyte, is particularly well-suited for this system. It can efficiently absorb excess nutrients from the water, improving water quality and promoting plant growth.
Moreover, halophytes are attractive sources of n-3 polyunsaturated fatty acids (PUFAs).
The Power of Compensatory Growth
Compensatory growth, a biological phenomenon where organisms grow faster after a period of food deprivation, can be leveraged to optimize fish and shrimp performance in aquaponics. By strategically implementing feeding and fasting cycles, growth rates can be enhanced, and feed costs reduced.
Feeding Regimes
According to the study published in the journal Applied Sciences, researchers established three autonomous systems, each operating with different feeding regimes:
- Daily feeding (Treatment A): Fish and shrimp were fed daily.
- Intermittent feeding (Treatment B): Fish and shrimp were fed three days a week, followed by four days of fasting.
- Extended fasting (Treatment C): Fish and shrimp were fed for seven days, followed by seven days of fasting.
Key Findings
The study yielded several important insights:
- Improved fish growth: Seabass in Treatment B, the intermittent feeding group, exhibited significantly higher growth rates compared to the other treatments. This suggests that periodic fasting can stimulate compensatory growth in fish.
- Enhanced feed efficiency: While Treatment B excelled in growth, Treatment A, the daily feeding group, showed a lower feed conversion ratio (FCR). This indicates that daily feeding may be more efficient in terms of feed utilization.
- Consistent shrimp performance: Baltic shrimp maintained steady growth and development across all treatments, indicating their adaptability to different feeding regimes.
- Enhanced plant growth: Salicornia plants thrived in Treatment B, the intermittent feeding group. This suggests that nutrient-rich water from fish and shrimp metabolism during feeding periods, combined with nutrient uptake during fasting periods, created optimal conditions for plant growth.
Implications for Brackish Water Aquaponics
These findings have significant implications for sustainable aquaculture:
- Reduced feed costs: Intermittent feeding can lower feed costs by minimizing feed waste.
- Improved water quality: The integration of halophytes can help purify water and reduce nutrient pollution.
- Enhanced biodiversity: Polyculture systems promote biodiversity and ecosystem resilience.
- Climate change adaptation: Euryhaline species are well-adapted to fluctuating environmental conditions, making them resilient to climate change impacts.
Conclusion
The study demonstrates the potential of Mediterranean euryhaline fish and halophytes in aquaponics to provide a sustainable and alternative approach to food production. Incorporating feeding and fasting cycles may be an effective feed management strategy, and food deprivation can have a positive impact on the growth of certain species.
Reference (open access)
Mitsopoulos, I., Papadopoulou, A., Vlahos, N., Berillis, P., Levizou, E., & Mente, E. (2024). Mediterranean Aquaponics: Fasting and Refeeding in a Polyculture Aquaponic System. Applied Sciences, 14(21), 9829. https://doi.org/10.3390/app14219829
