Molly Fish Gestation Period
A molly is pregnant for about 28 days, with a normal range of 20 to 40 days. Mollies are livebearers, so gestation is genuinely the right word: eggs are fertilised and develop inside the female, and she gives birth to 20-60 fry that swim from the moment they are born.
Signs a molly is pregnant
- The gravid spot near the vent darkens and enlarges over two to three weeks
- The abdomen becomes squared off rather than smoothly rounded
- Appetite rises early in the pregnancy and often drops sharply in the final days
- The female hides among plants, hovers near the heater or stays in a corner
- Shimmying and slow, deliberate swimming in the last 24 to 48 hours
Caring for a pregnant molly
Keep the tank stable at 25 to 27°C, feed small amounts of high quality food two or three times a day, and avoid large water changes late in the pregnancy. Add dense planting or a spawning mop rather than moving her to a breeding trap, which is stressful and can cause a premature drop. Once the fry arrive, remove the adults or move the fry, and feed crushed flake or infusoria several times daily.
Frequently asked questions
How long is a molly fish pregnant?
About 28 days. In a warm tank at 27 to 28°C it can be as short as 20 days, and in cooler water it can stretch to 40 days.
How many fry does a molly have?
Usually 20 to 60, and occasionally over 100 from a large, mature female. First broods are typically much smaller.
What is the gravid spot?
A dark patch near the vent that grows and darkens through pregnancy. In pale mollies it is the clearest sign that fry are developing.
Can a molly get pregnant without a male present?
Yes. Females store sperm for months and can produce several broods from a single mating, so a fish bought from a shop may already be pregnant.
Will the parents eat the fry?
Often, yes. Provide dense planting, floating cover or a separate nursery tank, and remove the adults once the fry are free swimming.