Introduction
This study is part of a larger project to improve the nutritional properties of freshwater and marine fish. The aim is to ensure the effective transfer of high-quality nutrient molecules from the processing of the raw material to the final product through the use of innovative, fortified feeds. The final aim is to deliver fish products with optimal nutritional value that fully meet consumer expectations.
Within this framework, the present study experimentally investigated the effects of enriching feed with algal oil on the physiology and health of a marine fish: Gilthead sea bream (Sparus aurata). Key evaluation parameters included growth performance, fatty acid profiles in the fillets, gut microbiota composition and intestinal short-chain fatty acid (SCFA) profile.
Materials and methods
The experiment was carried out with 360 gilthead sea bream, distributed over nine tanks (three tanks per feeding group), over a period of 15 weeks. The fish were fed a commercial control diet and two experimental diets containing algal oil in two different quantities. At the end of the feeding trial, samples were collected to analyze the composition and functionality of the gut microbiota using high-throughput sequencing techniques previously described in publications by our group (Terova et al., 2021; Hasan et al., 2024; Rimoldi et al., 2025). In addition, gas chromatography was used in conjunction with mass spectrometry to quantify short-chain fatty acids (SCFAs) in the intestinal lumen and to evaluate the fatty acid profile of the fillets.
Results
The inclusion of algal oil in the experimental diet led to an enrichment of omega-3 fatty acids, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), in the fillets of sea bream. Consistent with this increase, the ratio of omega-3 to omega-6 PUFAs was higher in the sea bream fillets fed the experimental diets. Overall, the fatty acid profile in the fillets matched that of the diets, which we have previously observed in a similar study (Terova et al., 2021). While the lipid composition differed, the lipid content of the fillets remained similar in the different feeding groups.
The composition of the gut microbiota remained largely unchanged in the feeding groups, suggesting that the addition of algal oil had no dysbiosis effects on the autochthonous microbiota. A higher proportion of algal oil in the diet led to a decrease in a few families comprising potentially pathogenic species. Interestingly, the concentration of butyric acid in the intestinal lumen of the fish belonging to the experimental feeding groups was lower than in the fish of the control group. This could indicate that either the addition of algal oil influences the production of butyric acid or improves the absorption of butyric acid, resulting in a lower accumulation in the lumen.
Conclusions
This study demonstrates the importance of the feed used in fish farming beyond the growth performance and health of the fish. In particular, it emphasizes the role of feed formulations in shaping the nutritional quality of farmed fish for human consumption. We have found that the addition of algal oil to gilthead sea bream feed increases the content of omega-3 PUFAs, important nutrients for human nutrition, in the filet without any negative effect on the health of the fish, particularly on the status of the microbiota. Most importantly, these results provide a basis for the next phases of the I-FISH project, where different additives will be included in fish feed to improve the nutritional value of the final product, i.e., the fish filet. Understanding how different nutritional strategies affect gut microbiota, metabolic outcomes and filet composition is essential for the development of more sustainable and nutritionally valuable aquaculture products.
Acknowledgements
Research was supported by the project: I-FISH. Protocollo nr: 414352—del 07/12/2023—AOO_IAI—AOO_Incentivi Fondo per la Crescita Sostenibile-Accordi per l’innovazione di cui al D.M. 31 Dicembre 2021 e D.D. 14 Novembre 2022.
References
Hasan, I., Rimoldi, S., Chiofalo, B., Oteri, M., Antonini, M., Armone, R., Kalemi, V., Gasco, L., & Terova, G. (2024). Effects of poultry by-product meal and complete replacement of fish oil with alternative oils on growth performance and gut health of rainbow trout (Oncorhynchus mykiss): a FEEDNETICSTM validation study. BMC Veterinary Research, 20(1). https://doi.org/10.1186/s12917-024-04324-0
Rimoldi, S., Quiroz, K. F., Kalemi, V., McMillan, S., Stubhaug, I., Martinez-Rubio, L., Betancor, M. B., & Terova, G. (2025). Interactions between nutritional programming, genotype, and gut microbiota in Atlantic salmon: Long-term effects on gut microbiota, fish growth and feed efficiency. Aquaculture, 596. https://doi.org/10.1016/j.aquaculture.2024.741813
Terova, G., Moroni, F., Antonini, M., Bertacchi, S., Pesciaroli, C., Branduardi, P., Labra, M., Porro, D., Ceccotti, C., & Rimoldi, S. (2021). Using Glycerol to Produce European Sea Bass Feed With Oleaginous Microbial Biomass: Effects on Growth Performance, Filet Fatty Acid Profile, and FADS2 Gene Expression. Frontiers in Marine Science, 8. https://doi.org/10.3389/fmars.2021.715078