Cultivated turbot were successfully spawned using sustained-release pellets containing a gonadotropin-releasing hormone analogue (GnRH-a), [d-Ala6–Pro9-Net]-luteinising hormone releasing hormone. Significant synchronisation of females was obtained, reducing the spawning season by about half. The number of spawning females was increased, and all sexually mature females ovulated. The delay between ovulations decreased from more than 2 days in controls to about 36 h in GnRH-a treated fish. The mean batch volume increased from 144 to 214 ml, but total volume of eggs for the whole spawning season did not change. At a production scale, fertilisation rate was significantly lower in the GnRH-a group than in the control (76.6 and 89.5%, respectively). Hatching rates were not significantly different between experimental groups.