Fatty acid profiles of two pelagic fish species in the NW Mediterranean: Reproductive and environmental implications

• We explore not only the total FA profile, but also the distribution of FAs across lipid fractions (reserve lipids, membrane lipids, and free fatty acids). • Significant maturity-stage differences in fatty acid profiles were observed in Scomber colias and Trachurus mediterraneus . • Reserve lipids were rich in SFAs and MUFAs. • Membrane lipids were dominated by PUFAs, particularly DHA (∼50 %). • FA analysis can offer valuable insights for fisheries management and environmental monitoring. The present study examines the fatty acid (FA) profiles of the Atlantic chub mackerel ( Scomber colias ) and the Mediterranean horse mackerel ( Trachurus mediterraneus ), from the NW Mediterranean, focusing on FA distribution across maturity stages in three lipid fractions: reserve lipids, membrane lipids, and free fatty acids (FFAs). Results show that the reserve FA fraction primarily influences the total FA profile during reproductive stages. PERMANOVA analysis indicated that 82.45 % of the variance was explained by species, lipid fractions, maturity stages and their interaction, with DHA, C18:1n-9, and C16:0 identified as key contributors. In total FA, the predominant FA were polyunsaturated FAs (PUFAs) (37.19–54.72 %). The highest values for monounsaturated FAs were found in the reserve FA fraction (20.17–38.27 %). PUFAs were predominant in the membrane lipids (>60 % for each species), especially DHA (49.89–56.51 %) and were also substantial (27.68–43.10 %) in the reserve lipids. Saturated FAs were predominant in the FFA fraction (48.84–64.77 %). A comparative analysis with other small pelagic fish in the region addresses the influence of environmental factors, seasonality, and feeding strategies in lipid profiles of pelagic fish in the NW Mediterranean. These findings contribute to our understanding of how environmental stressors, such as rising sea temperatures, affect the health and condition of marine fish, with broader implications for marine food webs and trophic interactions in a changing climate. The results also support that monitoring PUFAs (particularly EPA and DHA) in pelagic fish could serve as indicator of the health of both the stock and the pelagic environment they live.