Molly fishes are a type of guppy that give birth to live babies instead of producing eggs like other fish. Breeding occurs often in molly fish; even when there is no male in the tank for several months, the female will release babies at least once a month. It is important to identify when a molly is pregnant and know the approximate time the babies will be born. This is so you can protect the babies after birth because mollies have a tendency to eat their young.
Watch your pregnant molly for any behaviour changes. Some changes include moving slower, staying away from other fish in the tank and eating less.
Track the days since you noticed your molly was pregnant. A typical gestation period is around 60 days.
Note if the dark triangular spot near the anal vent has got bigger and darker in colour. This indicates that labour and birth are near.
Look for changes in your molly's stomach and overall girth. Pregnant and near-labour mollies are much bigger in the middle and look stretched out.
When it begins to get close to the 60-day mark, move your pregnant molly to a breeder net to protect both the mother and her babies. Once the molly has released her babies, move her back to the main tank and leave the babies in the breeder net until they get bigger and are no longer in danger from the other fish. Watch your molly throughout her pregnancy and as she goes through several pregnancies within a few months. As you observe, you will begin to notice the changes she goes through as she gets closer to releasing babies and you'll be able to notice more quickly when it's about to happen.