How can one fertilization produce several broods in guppies, mollies, and swordtails?

In guppies, mollies, and swordtails—which belong to the group of live-bearers within the family Poeciliidae—a single fertilization can result in multiple broods because the female is capable of storing sperm.1

Following a successful mating, the female retains the sperm within her body, allowing her to fertilize subsequent batches of eggs internally over time. Consequently, these fish can produce a series of broods, typically at approximately monthly intervals, without requiring a new mating encounter for each reproductive cycle. In these species, the young are born fully developed, providing a survival advantage by reducing their vulnerability compared to egg-laying species.12