This article describes the effects of food availability on the sexual maturation of Ruditapes decussatus through histological examination of the gonadal tissue. Three food rations were tested: High (H: 1 mg. organic matter. g live weight–1.day-1 of the microalgae Isochrysis galbana clone T-ISO), intermediate (I: 0.5 mg OM g live weight-1 day-1) and nutritionally restricted (R: 0.25 mg OM g live weight-1 day-1). The tests were carried out at a constant temperature of 18°C for a period of 70 days for diets H and I, and 120 days for diet R. The results showed that in R. decussatus the energy from ingestion was mainly channelled to reproductive processes, especially when food was restricted. The clams matured sexually under all the conditions tested, both with a somatic growth and with a loss of body mass. The available food was directly related to the rate of the gonadal development and with the total quantity of gonad generated. Equally, food restrictions limited gonadal recovery after spawning episodes. Food quantity also affected the dry weight of soft tissues (DW), which increased with the highest ration (H) and decreased notably with the lowest ration (R). Decreases in DW when food was scarce appeared to be more related to loss of reserve tissue rather than to variations in the quantity of reproductive tissue.