Pregnant Molly Fish: Beginners’ Guide To Mating & Breeding

pregnant molly fish
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Last Updated: February 20, 2023 by Dave Gibbins

Mollies reproduce several times a year. In fact, they are amongst the easiest fish species to breed.

If your tank consists of male and female mollies, they will spawn naturally under the right conditions. But, if the fries live in the same tank as adult mollies, they are less likely to reach maturity.

To raise molly fry, you should learn how to identify pregnant molly fish and how to care for them. This article discusses this at length.

How Do Molly Fish Breed?

yellow and black mollies in a fish tank

Breeding molly fish is an achievable task, even for beginner aquarists. Mollies breed easily, so be prepared to raise numerous babies all year.

Mollies do not lay eggs like other fish breeds. Instead, they give birth to live fish. Male mollies fertilize the eggs when they are in the female’s belly. The female molly can store sperm and continue giving birth without having to mate.

Molly fish’s pregnancy cycle lasts between 40 to 60 days.

The fertilized eggs hatch after 45 days prompting the female to release the live molly babies.

But, how can you tell a molly fish is pregnant? Read on.

Molly Fish Pregnancy Stages

Pregnant molly fish undergo various stages before they give birth. The gestation period features conception, embryo formation, development of fry, pre-birthing, and actual birthing stages.


yellow mollies mating in a fish tank

Conception is relatively easy if you have male and female mollies in your aquarium. Besides, female mollies store sperm from a single mating and fertilize their eggs every month.

Embryo Formation

After fertilization, the eggs begin to form an embryo. This happens about 7 days after conception, and it becomes easier to see the gravid spot.

Embryo Develop Into Fry

The embryos now develop into molly fry as the pregnancy advances. This development causes the pregnant molly’s belly to swell.

Pre-Birthing Stage

At this stage, the fries are fully developed and about to be delivered. If you watch the pregnant fish closely, you might see the fry eyes in their mothers’ belly.

Birthing Molly Fries

Mother molly gives birth to live fish. These little guys can swim as soon as they are delivered. But, you need to save molly fry from their mothers as they will gladly eat them.

How To Identify Pregnant Molly Fish

pregnant molly in fish tank

Pregnant molly fish do exhibit pregnancy signs. The good news is these physical and behavioral signs are not difficult to spot.

A Swollen Belly

Male molly fish have a torpedo-shaped body, while females have a naturally prominent belly. During pregnancy, molly’s belly becomes thicker and more square. You will notice that the mother’s belly will seem stretched out a few weeks after fertilization.

Mollies can give birth to up to 100 baby mollies, which explains their rounded belly during pregnancy.

Dark Gravid Spot

Livebearers have a gravid spot right close to the anal vent. This spot grows larger as a female is about to give birth.

In the beginning, pregnant molly fish have a blackish mark on their gravid spot. As time progresses, this mark becomes more evident, especially in lighter-colored mollies. However, you may have difficulty finding this spot in black mollies.

Aggression And Withdrawal

You can also tell a molly fish is pregnant if she exhibits signs of aggression and isolation.

Pregnancy drives them into being overprotective of themselves.

But they usually do not harm other tank mates when doing so.

As the pregnant female molly is about to give birth, she spends her days hiding. These fish feel more comfortable and secure in their hiding spots.

You can keep your pregnant molly fish comfortable by moving them to a separate tank. If you do not have a separate tank, consider adding more live plants or plant decorations to provide privacy.

Increased Appetite

different species of molly in fish tank

Pregnant mollies have an increased appetite to match the extra energy their bodies need to nurture the fry. Mollies become more active during feeding times and may start competing for food.

Since the dramatic appetite change is due to pregnancy, ensure your molly fish are well fed.

But, the increased appetite phase does not last long. Instead, it decreases as labor approaches. Your pregnant mollies will have less preference for food and more for isolation.

Crave Warmth

Mollies are tropical fish that thrive in warm water temperatures. It is no wonder that pregnant mollies seek warmth.

You may notice female mollies swimming close to the heating element or the overhead UV light.

We recommend that you maintain consistent temperatures throughout the gestation period. Doing so guarantees good health for the female molly fish and the tiny fry.

How To Care for Pregnant Molly Fish

Pregnant mollies do not need much care during pregnancy. But you can keep the pregnant molly fish happy by providing an ideal environment. Besides, stress can drive your molly into aborting her own fry.

Separate Pregnant Molly

orange molly on black background

Pregnant mollies withdraw from other fish when they are about to give birth. So, separate pregnant mollies from other fish to keep them happy and relaxed. Besides, it prevents the adult fish from eating her fry.

You can move the female molly to a breeding box or a separate tank. During the transfer, use water from the main aquarium to prevent sudden water changes.

Provide A Warmer Environment

Warmer temperatures will keep the female mollies more comfortable. Keep the temperatures between 79 and 81 degrees Fahrenheit.

Provide Hiding Spaces

Add lots of live plants and decorations to provide extra hiding spaces for the pregnant molly. Mollies love darker spots when they are close to giving birth.

How To Tell A Pregnant Molly Is About To Give Birth

When a pregnant molly is about to release her live young, her gravid spot becomes darker and more visible. At this point, the fry eyes are more noticeable.

The female will seek refuge in darker places in the fish tank.

She will stay away from other fish, have a reduced appetite, and exhibit signs of lethargy. If the tank is heavily planted, you may have trouble spotting the female, and she may hold back from feeding.

In addition to their rounded bellies, female mollies fill out beneath their gills because the womb is fully stretched.

Also, adult mollies rarely shake their tails unless the tank water is too acidic. But, pregnant mollies shake their tails when they are about to give birth. This action is often due to the stress associated with giving birth.

How To Save Molly Fry

mollies fry image

Molly fry needs protection from their mother and adult fish. Their small size makes them prey to other fish. To save the baby fry, do the following:

Place Pregnant Molly In A Separate Tank

Remove the pregnant mom from the main tank to save molly’s fries. If you keep the pregnant mother in the main tank, most of her babies will get eaten by adult mollies.

The new tank also offers more swimming space and freedom for the fry.

Remove The Mother From The Breeding Tank

Once the mother molly releases her live young, remove her from the breeding tank and back to the main tank. Molly females will eat their own babies a few minutes after giving birth. So, always keep the fry separate from all adult fish.

Add Lots Of Plants

If you do not have a separate tank or breeding box, provide hiding spots for the fry. You could add live plants, caves, rocks, and décor to keep the fry safe from the adults. Include a few floating plants like java moss, duckweed, or hornwort.

How To Care For Molly Fry

You need to take care of the molly fry, whether in the main tank or a breeding box. For starters, maintain the temperature between 72 and 78 degrees F. An aquarium heater will help keep the fry warm.

Next, install a sponge filter to remove debris from the water. Moreover, this filter will not suck these little guys. Also, ensure the ammonia and nitrate levels remain at 0 ppm.

To feed baby molly fish, offer brine shrimp, daphnia, bloodworms, microworms, vinegar eels, powdered fry food, or crushed flake food.

These foods should fit into the fries’ tiny mouths. Depending on how many fry you have, feed them 3 to 5 times a day.

Here is a YouTube video that details molly fry’s care:

Related Questions

How Long Do Molly Fish Stay Pregnant?

The gestation period for mollies is 45 to 60 days. Plus, since female mollies can fertilize their eggs every 30 days with the sperm they store from the male molly, they always seem pregnant.

Can Mollies Breed With Guppies?

Yes, these livebearers can crossbreed because they belong to the same species. Mollies and guppies create hybrids Golly and Muppy.

Do Molly Fish Give Birth At Night?

Yes, most mollies give birth at night. Nevertheless, some give birth during the day as long as their tank is dark.

How Many Babies Do Molly Fish Have?

When breeding mollies, expect to raise 20 to 100 young mollies at a time.


I believe you can now tell when your molly fish is pregnant and when they are about to give birth.

Female molly fish exhibit behavior signs like increased appetite and aggressive behavior when pregnant, and physical signs like rounder bellies.

When these fish are about to give birth, their appetite decreases, and they become more withdrawn. Provide adequate hiding spaces to calm your mollies during this time.

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