Sea bass (Dicentrarchus labrax), turbot (Scophthalmus maximus) and gilthead sea bream (Sparus aurata) spawners were kept in 2 identical 40 m3 tanks, one outdoors (control) and one indoors (test) during a 5-year experiment. The control tank was under natural yearly photoperiod and the temperature cycles of western Brittany. The test tank was under similar variation for 3 years but with the cycles compressed into 10 months. The 3 species spawned naturally in these artificial conditions at various stages of the experiment. After 3 years, the fish in the test tank spawned an average 5 months ahead of the others. [NOT CONTROLLED OCR]