The effect of photoperiod on survival and growth of cultured young soles ( Solea solea) was investigated from hatching to the age of three months, at 18° C. Two experiments were performed, comparing days with 12, 18 and 24 h light. The fishes were reared in 60 1 tanks, conical ones before metamorphosis, square ones with a sandy bottom from metamorphosis to the age of three months. They were fed on live food organisms for 1 month, on frozen flesh of the bivalve Laevicardium crassum for the two other ones. During the larval period, no significant difference was recorded in the survival rate but a better growth was obtained with 18 and 24 h light, suggesting a predominant diurnal feeding. From metamorphosis to the age of three months (mean weight: 1 g) no significant effect of the photoperiod on the survival and growth of the juveniles could be demonstrated.