This study investigated the mode of egg production in the spotted seahorse Hippocampus kuda to determine when females are receptive to mating. There were two distinct groups of oocytes in the ovary, the first a cohort of extremely small oocytes, and the second a cohort of oocytes that increased in size with time. Ovulation occurred once before spawning, and only oogonia and oocytes in early developmental phases remained in the ovary after spawning. The presence of a synchronous group of growing oocytes indicates that the mode of egg production in H. kuda is of the group-synchronous type.