Introduction
The use of sustainable aqua feed ingredients in aquaculture primarily aims to reduce pressures on marine ecosystems by minimizing the reliance on fish meal and fish oil production. Most sources of omega-3 fatty acids (FA) come from highly exploited marine resources; however, omega-3 FA display a pivotal role in marine aquaculture. In the search for environmentally friendly and economically viable feed ingredients, terrestrial plants sources have emerged as promising alternatives to traditional marine-based inputs, but feature several limitations (e.g., limits of incorporation, anti-nutritional effects…) . Th e present study evaluated the effects of different plant-based diets on the fatty acid profile of the marine amphipod Gammarus locusta , a key species in marine trophic chains and a potential candidate for inclusion in marine aquafeeds due to its content in long-chain polyunsaturated fatty acids (PUFA). This approach aims to further merge green and blue food ecosystems.
Material and methods
Offspring of G. locusta were fed with four different diets: Ulva sp. (Ul) (used as control), peas (Pe), green beans (GB), and carrots (Ca) , until reaching sexual maturity . Subsequently, individuals were collected, and their fatty acid composition determined. Fatty acid methyl esters were analysed via gas chromatography- mass spectrometry (GC-MS) . The absolute abundance of fatty acids was calculated in µg/mg dry weight (DW), and data were compared across different diets.
Results
The fatty acid composition of G. locusta clearly reflected their diets . Amphipods fed Ulva sp. showed higher levels of eicosapentaenoic acid (EPA) (C20:5n-3) (Ul: 1.3 9 ± 0.15, Pe: 0.70 ± 0.18, GB: 1.15 ± 0.32 and Ca: 0.68 ± 0.09, µg/mg DW) (Figure 1) . However, in the case of docosahexaenoic acid (DHA) (C22:6n-3) , amphipods fed Ulva displayed lower values when compared to conspecifics fed plant-based diets (Ul : 0.26 ±0.07 , Pe: 0.28 ± 0.09, GB: 0.46 ± 0.08 and Ca: 0.41 ± 0.08 µg/mg DW) (Figure 1) . It is worth highlighting that amphipods fed on terrestrial plant diets (Pe, GB, Ca) exhibited both EPA and DHA, despite the absence of these fatty acids in their diets
Discussion
These findings highlight the metabolic plasticity of G. locusta and its potential ability of synthesis ing long-chain omega-3 PUFAs, such as EPA and DHA from diets without these fatty acids . Although marine ingredients like Ulva sp. can directly supply EPA (in residual amounts) , terrestrial diets enable biosynthesis of EPA and DHA, offering a sustainable strategy to farm G. locusta, whose biomass can eventually be used as a n ingredient/supplement for aquafeeds . This approach is a promising pathway for converting low-cost, terrestrial inputs into high-value marine ingredients through bioconversion.
Conclusion
G. locusta can biosynthesis e essential n -3 PUFAs (namely EPA and DHA) from terrestrial plant-based diets, making them viable and sustainable inputs for producing enriched live feeds. The use of terrestrial diets represents a novel and ecologically sound approach for generating DHA and EPA through trophic upgrading.
Acknowledgements
This study was performed under the scope of project “BLUE BIOECONOMY PACT” (Project Nº. C644915664-00000026), co-funded by the Next Generation EU European Fund, under the in-centive line “Agendas for Business Innovation” within Component 5—Capitalization and Business Innovation of the Portuguese Recovery and Resilience Plan (RRP), as well as under the scope of project “PUFAPODS Merging blue and green food systems - Using marine gammarid amphipods supplied with plant food processing side streams to produce n-3 LC-PUFA” which is supported by FCT/MEC https://doi.org/10.54499/2022.01620.PTDC. We also thank the financial support to UID Centro de Estudos do Ambiente e Mar (CESAM) + LA/P/0094/2020 through national funds.