Long-chain omega-3 polyunsaturated fatty acids (n-3 PUFA) are involved in the structure and the function of all living organism's membranes, and thus play a key role in several physiological functions. Capacities of n-3 PUFA synthesis by marine fish species are limited, but are expected to fluctuate depending on fish life histories and environmental factors. The aim of this study was to measure the variability in n-3 PUFA composition in the liver of European seabass Dicentrarchus labrax, according to life stage and habitat. We sampled fish from three different life stages (first, second and third year, i.e. G1, G2, and G3 respectively) in two French estuaries (Seine and Loire). Juveniles were weighted and measured to obtain their condition factor, and their hepatic fatty acid composition (FAC) was analyzed in both neutral (NL) and polar lipids (PL) by gas chromatography (GC-FID). Condition factor did not differ between groups, but liver FAC differed between sites at the youngest stage of life (G1). PUFA proportions (in percentage of total FA), mainly represented by the 22:6n-3 fatty acid (docosahexaenoic acid; DHA), were higher in the G1 from Loire than in the G1 from Seine for both NL and PL. The opposite result was observed for the monounsaturated fatty acids (MUFA), mainly represented by the 18:1n-9 FA. These results may be related to the differences in fish trophic ecology between the two estuaries and/or to difference in their PUFA biosynthesis capacities depending on their age.