Under natural external conditions in Brittany, ovulation and spermiation have been induced in summer after the photoperiodic treatment of a strain of rainbow trout (Salmo gairdneri ) (normal reproduction in winter). The following results have been obtained: (1) All females and males have produced gametes the summer following their 1st or 2nd reproductive season. (2) The absolute fertility of females after advanced spawning did not significantly differ from that obtained during the normal winter spawning period. (3) Eggs quality depends upon the water temperature during spawning, which must be under 15 degree C. (4) The growth of summer fry is similar to that of winter fry. (5) The additional summer reproduction did not alter the eggs quality of the following winter spawning. (6) There was no significant difference between the quality and quantity of eggs obtained either after hormonal synchronization of summer or natural ovulations.