Molly fish are typically pregnant for around 60 days. The gestation period may vary between various molly species, but they’re usually pregnant for 50-70 days.
Molly fish use internal insemination when mating, so females will carry eggs during the gestation period. Once the gestation period is finished, the female molly will release the fry into the water. Each molly fish can release around 10-60 fry at once, with more experienced mothers usually releasing more babies than new mothers.
Additionally, molly fish can get pregnant again right after releasing their fry. A female molly fish can store sperm for months to fertilize their eggs, even if there are no males present in the tank.