The aim of this study was to analyse the concentration of mercury (Hg) in the muscle of a common littoral, omnivorous fish such as the white seabream, Diplodus sargus, and to evaluate its relationship with the age and size of the specimens. Large, older predatory fishes have typically been the main target species for risk assessment of Hg intake in humans. The white seabream is neither a big fish nor a predator, but all sizes of NW Mediterranean specimens of this species showed high levels of Hg, with clear increases in older specimens. In addition, although the Se:Hg molar ratio was high and could reduce the impact of high concentrations of Hg in smaller fishes, it could not in the older specimens of D. sargus analysed because it decreased with age. This is not a major concern for human health because the white seabream is not a widely consumed species. However, in special situations involving toddlers, children and women of childbearing age, problems might arise if the white seabream or similar species are consumed in place of those that current recommendations advise against eating. In these cases it is very important to consider the species of fish consumed in each country and carefully assess the risk of Hg intake