Instructions
Determine the age of your female fish. Mollies can be ready to breed at as young as four weeks of age.
Examine the fish regularly. Once a female has mated, the fertilized eggs take about four weeks to mature. A pregnant female's body will begin to swell in the abdominal area. As she gets larger, the gills may appear distended.
Watch the rear abdomen for a dark spot. This is known as the gravid spot. It appears because the brood of babies has grown so large that they push part of the mother's abdominal lining tightly against the skin. Once this spot appears, your molly is likely to have her babies within a few days. Mollies can have anywhere from a few to several dozen young.
Provide cover if you want to keep and raise the baby fish (called "fry"). They are vulnerable to being hunted and eaten as soon as they are born -- even by their own parents! Place heavy plants in the tank -- this will give the fry places to hide from bigger fish. Or, you can move the expectant mother to another tank by herself, or use a tank divider to separate her from the other fish.
How to Know if a Molly Is Ready to Have Babies
The molly is a popular breed of freshwater aquarium fish. Mollies are livebearers, which means their eggs are fertilized and mature inside the mother's body. After the gestation period is complete, the mother fish releases her babies into the water.