Given that sea urchins eggs and larvae have been proposed as putative prey in marine larviculture, broodstock rearing conditions must be optimized for this purpose. In the current study, adult sea urchins Paracentrotus lividus were reared in 400-L tanks for 5 mo under 4 stocking densities (100, 200, 300, and 400 sea urchins/m² of tank base area) to determine their effect on spawning performance and fertilization rate, and on broodstock month relative growth. For all stocking densities, more than 60% of sea urchins induced to spawn released a large number of gametes (more than 200 × 10⁶ spermatozoa or more than 500 × 10³ eggs per spawning). The percentage of males with large emissions was higher at a density of 300 sea urchins/m². Irrespective of broodstock stocking density, fertilization rate was always higher than 90%. Lower relative growth was recorded with densities of 300 sea urchins/m² and 400 sea urchins/m² compared with 100 sea urchins/m². We conclude that under the rearing conditions adopted in this study, captive P. lividus broodstock can be at least reared up to 400 sea urchins/m² without impairing reproductive performance.