A 4-wk rearing trial of the sea urchin Paracentrotus lividus was carried out in a closed-circuit system in the presence and absence of food supply to evaluate the short-term response of gametogenesis to different feeding conditions. At the end of the trial, the gonad index (GI) was calculated, histological analyses of the gonads were performed, gamete fertilization ability was evaluated, and sperm motility was assessed by computerized motility analysis. Starvation significantly affected gametogenesis, whereas developing gametes were always observed in fed animals, whose GI had doubled by the end of the 4-wk trial. No differences were recorded between gametes from reared (fed) urchins and wild-collected ones. Although spent gonads frequently contained unspawned motile spermatozoa or morphologically intact eggs, the fertilization ability of gametes from starved urchins was significantly lower. It may be concluded that, although they were at the end of the reproductive season, the specimens fed ad libitum were able to reactivate the gamete maturation process immediately. This ability can be used in short-term procedures for roe enhancement and gamete production, particularly for specimens from areas in which environmental conditions determine slow gametogenesis and a consequently short reproductive season.