Introduction
Aquaculture is crucial for global food and livelihood, with over half of fish for human consumption coming from aquaculture in 2014 (FAO, 2022). By 2030, production is expected to reach 93.6 million tons, a 25% increase. Intensive aquaculture, using Recirculating Aquaculture Systems (RAS), ensures continuous quality fish production. RAS polyculture, cultivating multiple species together, improves resource utilization, waste management, and productivity (Verdegem et al., 2023; Zhang et al., 2011; Zhang et al., 2023). This study examines the impact of using a common pellet in RAS for breeding pikeperch (Sander lucioperca) and Russian sturgeon (Acipenser gueldenstaedtii), focusing on nutrient transfer efficiency, lipid, fatty acid, and amino acid utilization, and variations in nutrient absorption and flavor profiles.
Materials and Methods
All experimental groups were replicated three times. Juvenile pikeperch and Russian sturgeon were reared using pond and intensive aquaculture, respectively. A total of 1224 pikeperch and 576 sturgeons were divided into five groups: monoculture pikeperch (P100), monoculture sturgeon (P0), and three mixed stocks with varying pikeperch-to-sturgeon ratios (P90, P80, P70). Fifteen tanks, each containing 120 fish with an initial biomass of 5.75 kg/m³, were used. Fish were evenly distributed by age, with initial body weights of 18.17±2.65 g for pikeperch and 18.23±3.62 g for sturgeon.
Fish were fed Skretting Europa 15 F floating feed (2 mm pellets), containing 55% crude protein, 16% crude fat, and 4637 kcal/kg digestible energy. Feeding was administered three times daily using automatic feeders. A 12-hour photoperiod was maintained throughout the experiment. The introduction of sturgeon did not significantly affect water quality, demonstrating their compatibility with sustainable aquaculture.
Suspended solids were measured every 28 days, and tanks were cleaned and drained using aquatic nets. Fish were sedated with tricaine mesylate (MS-222) before biometric measurements. Samples, including fish fillets and suspended solids, were collected, filtered, and stored at -18°C for analysis. A total of 45 samples were analyzed using advanced laboratory instruments at the Laboratory of Nutrition.
Amino acid analysis involved protein digestion, derivatization with dansyl chloride, and HPLC-UV detection. Methionine and cysteine were quantified as methionine sulfate and cystic acid, respectively. Lipid extraction was conducted using hexane-isopropanol, and fatty acid composition was determined by gas chromatography. Acid-insoluble ash was used to assess lipid digestibility, providing a reliable alternative to traditional methods.
Results
The amino acid profile of pikeperch fillets in monoculture and polyculture with Russian sturgeon showed that lysine reserves were lower in polyculture, while methionine reserves increased. Non-essential amino acids like glycine and proline were highest in the P90 polyculture combination. Fillet lipid content and fatty acid profiles did not show significant changes between monoculture and polyculture. The DHA to EPA ratio almost doubled in flesh compared to food across all groups. Lipid digestibility of the common pellet was excellent, with the highest lipid-ADC in the P70 polyculture tank. EPA and DHA content in pikeperch fillets were lower than in Russian sturgeon, with no significant difference between monoculture and polyculture treatments.
For Russian sturgeon, no significant changes in lysine or methionine reserves were observed between monoculture and polyculture. The fillet fat content increased significantly in polyculture, with higher MUFA oleic acid content. Lipid digestibility was excellent across all groups, with the highest lipid-ADC in monoculture tanks. EPA and DHA content in Russian sturgeon fillets were higher than in pikeperch, with the highest content in the P70 polyculture tank.
Discussion
The study examined the effects of polyculture on the amino acid and lipid profiles of pikeperch and Russian sturgeon in RAS. Key findings highlight the nutritional value, flavor, and texture of the fish. Acid-insoluble ash was found to accurately predict lipid digestibility, offering a reliable alternative to traditional methods. Pikeperch in polyculture showed decreased lysine and increased methionine reserves, while sturgeon amino acid profiles remained stable. Lipid content in pikeperch fillets was unchanged, but sturgeon fillets had higher fat content in polyculture. Lipid digestibility was excellent across all groups, with sturgeon showing robust lipid digestion. DHA and EPA content in pikeperch was similar in both monoculture and polyculture, while sturgeon in polyculture had higher MUFA and DHA content. The study demonstrates the benefits of RAS polyculture in enhancing nutrient utilization and improving fish nutritional quality. Further research is needed to explore the effects of polyculture on fish growth, health, and environmental sustainability in RAS systems.
Acknowledgements
This research was funded by the Ministry of Agriculture of the Czech Republic (project NAZV QK22020144) and the Ministry of Education, Youth and Sports of the Czech Republic through the CENAKVA project (LM2023038). The second author gratefully acknowledges support from the Czech Science Foundation (GAČR 22-18597S) for the analysis of fatty acids and amino acids, aimed at investigating nutrient bioaccumulation in fish. Additionally, part of this work was conducted with the assistance of the VVI CENAKVA Research Infrastructure (ID 90238, MEYS CR, 2023–2026).
References
FAO, 2022. The State of World Fisheries and Aquaculture 2022. Towards Blue Transformation, In Brief to The State of World Fisheries and Aquaculture 2022. FAO, Rome. https://doi.org/10.4060/cc0463en
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Zhang, R., Chen, T., Wang, Y., Short, M., 2023. Systems approaches for sustainable fisheries: A comprehensive review and future perspectives. Sustainable Production and Consumption 41, 242–252. https://doi.org/10.1016/j.spc.2023.08.013
Zhang, S.Y., Li, G., Wu, H.B., Liu, X.G., Yao, Y.H., Tao, L., Liu, H., 2011. An integrated recirculating aquaculture system (RAS) for land-based fish farming: The effects on water quality and fish production. Aquacultural Engineering 45, 93–102. https://doi.org/10.1016/j.aquaeng.2011.08.001