Before giving birth, a pregnant mollie begins swimming and hiding among the aquarium plants and rubbing her enlarged belly on the leaves. She also develops a dark spot near her anal fin. The gestation period for mollies is 28 days.
Because most livebearers will eat the baby fish, or fry, remove the mollie from the main tank and place her in a breeding tank. The new aquarium needs a filtration system and heater. Allow the plants to float at the top of the tank and do not add gravel.
As soon as the mollie finishes giving birth, remove her from the aquarium. Otherwise, she will eat the fry.