Introduction
The accelerated growth of marine aquaculture created an urgent need for sustainable and quality ingredients to maintain the performance and nutritional value of farmed species. Marine gammarid amphipods can be an excellent source of essential fatty acids, namely long-chain n -3 polyunsaturated fatty acids (LC-PUFA). However, their potential contribution to the formulation of aquafeeds still remains largely unexplored. The present work evaluated the effect of mono-specific macroalgal diets on the fatty acid composition of the offspring of Gammarus locusta fed on these macroalgae and compared it with the offspring of wild conspecifics.
Materials and methods
Gammarus locusta breeding pairs were fed one of five mono-specific macroalgal diets ( Ulva sp., Fucus sp., Laminaria sp., Gracilaria sp., and Chondrus sp.), and their broods were collected to determine their fatty acid composition using gas chromatography-mass spectrometry (GC-MS) . Subsequently, their FA composition was compared with that displayed by the offspring of conspecifics from the wild.
Results
The offspring from wild G. locusta showed the highest amount of polyunsaturated fatty acids (PUFA) (4.95 ± 0.31 mg mg-1 DW), as well as essential fatty acids, namely eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n -3), with an abundance of 2.49 ± 0.21 and 0.87 ± 0.16 mg mg-1 DW, respectively. The algal treatment that promoted the highest PUFA cont ent in offspring was Fucus sp . (4.46 ± 0.31 mg mg-1 DW), but those derived from broodstock fed with Chondrus sp. showed the high est DHA levels (0.56 ± 0.10 mg mg-1 DW) . However, no significant differences in fatty acid composition were found between offspring from broodstock fed with the different mono-specific macroalgal diets . On the other hand, the abundances of stearic acid (18:0) and DHA were significantly higher i n the offspring of adults from the wild when compared to those fed on algal-based diets.
Discussion
These findings suggest that G. locusta selectively conserves and biosynthesises essential fatty acids for growth and reproduction, particularly LC-PUFA. However, this process remains to be demonstrated in marine gammarids, as the presence of genes encoding the front-end desaturases necessary to LC-PUFA biosynthesis is yet to be described in their genome. Moreover, this experiment highlighted the importance of maintaining optimal diet properties for gammarid cultivation , as some mono-specific diets may negatively impact their reproductive yield. Nonetheless, all the offspring analysed present a balanced fatty acid composition with potential applications for aquaculture.
Conclusion
Gammarus locusta offspring present a balanced FA profile with potential applications for aquaculture, as they demonstrate a remarkable trophic plasticity by being able to feed on a wide variety of substrates. Further research is needed to fully elucidate the mechanisms underlying trophic upgrading in gammarids. By using both marine and non-marine diets, as well as nutritional programming and selective breeding , it is possible to establish lineages that match or even surpass the fatty acid composition of wild conspecifics.
Acknowledgements
This study was performed under the scope of the project “BLUE BIOECONOMY PACT” (Project Nº. C644915664-00000026), co-funded by the Next Generation EU European Fund, under the incentive 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 the 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.