Seasonal changes in somatic condition, hepatic and gonad activity, as well as their effects with age and sex were examined in Atherina boyeri from the Mar Menor coastal lagoon (SE Spain). Seasonal cycles of somatic condition, hepatic and gonad activity were similar in both sexes, consisting of three phases. Somatic condition increased during summer, remained constant from autumn to mid-spring and decreased from mid-spring to the beginning of summer, coinciding with reproduction. Hepatic activity remained constant from mid-summer to winter, increased sharply from winter to spring and decreased during the spawning period, which lasted 4-5 months (similar to other Mediterranean locations). These cycles suggest that the species is well adapted to local conditions, ensuring reproductive success without endangering individual survival.