Pregnant Molly Fish – Is Female Molly Fish about to Give Birth?

If you’ve gotten down the science of raising molly fish, you may be ready for the next step in your adventure of keeping mollies – breeding them.

by Fabian

Updated: July 4, 2019 / 7 mins read

Fabian is the dedicated Chief Editor at Aquarium Nexus. From a young age, he was captivated by the vibrant world of aquatic life, leading him to accumulate over 20 years of experience in keeping and breeding various fish species. The fulfillment derived from the aquarium hobby has remained a constant throughout Fabian's life. As an expert in the field, he finds great pleasure in imparting his extensive knowledge and personal experiences to both seasoned aficionados and budding enthusiasts.

You may find the idea intimidating at first, but don’t worry, breeding mollies is both easy and a very rewarding experience that I will help you navigate.

This article can serve as a quick go-to guide on spotting the signs of molly pregnancy, saving molly fry, and feeding and caring for baby molly fish.

How Molly Fish Breed?

Molly fish are livebearers, which simply means that instead of laying eggs, fertilizing them on the spawning site and hatching them, molly fish give birth to live fish.

While not immediately active, molly juveniles will be able to swim and feed in a matter of hours from birth.

Reproductive age is reached at 12 months for molly males and 6 months for molly females.

Be careful about male to female ratio. Male molly fish can stress out females with their constant pursuit.

Keeping one male with three females is the recommended ratio for breeding these fish, any more will create too many pregnant molly fish and too many molly babies as a result.

You may notice the male molly fish under the female molly, which is how they copulate. The female can store the sperm of the male for months, which means that she’ll be able to give birth multiple times even if no males are present in the tank.

The female molly stores the fertilized eggs inside her body until they hatch and only then does she release the fry into the tank. The gestation period varies but it’s around 45 days on average.

Mollies can breed up to 100 fry at one time plus they breed quite often, so expect a lot of fry if you attempt to breed them.

While they do produce a lot of fry, they’re also very bad at keeping them alive. Adult mollies don’t care for their fry and they’ll eat them if they’re not separated from them.

To save molly fry, the best is to separate the pregnant female molly from the rest of the fish right before she’s about to give birth.

To be able to do this, however, you must know how to spot the signs that your molly fish is pregnant.

How to Know if Molly Fish is Pregnant?

If you’ve watched your molly fish closely, you may have noticed their behavior during courtship and copulation.

After reproduction, it will take your mollies a couple of weeks until they give birth.

If fertilization was successful, you will notice changes in your female molly during the gestation period. Some signs are physical, others are behavioral.

Physical signs that your molly fish is pregnant:

• Changes in color – Colorful molly breeds will develop a black line on their lower bellies;
• Swollen belly – On some molly fish (e.g. black mollies), it’s hard to spot the black line, but you’ll notice they look plumber and their bellies are swollen when they’re pregnant.

As molly fish are about to give birth, they’ll start to show some behavioral signs too, which will be a good indication for you to remove the female molly from the tank and transfer her to a different tank.

Is Molly Fish About to Give Birth?

It’s difficult to tell when exactly when your molly fish will release baby mollies. Aquarists breeding mollies often report seeing the female molly fish develop a V-shape at the bottom of her stomach as she’s about to give birth.

In my experience, however, pregnant molly fish will become more reclusive and will seek out darker areas of the aquarium as they’re preparing to give birth.

Therefore, it’s important to have enough live plants in your aquarium that will provide coverage for your pregnant molly fish and make her feel secure and comfortable.

If you notice these behavioral signs in your molly fish, you can separate her from the rest of the adult fish. This will help you to better manage the fry and save them from hungry adult fish.

How to Save Molly Fry?

Adult mollies – but other fish too that you may keep with your mollies – will not shy away from eating their own fry if they’re not removed from their tank.

With livebearers this is a very common occurrence, so you needn’t worry that something is wrong. It simply doesn’t register for them that they’re parents and they easily mistake their own fry for food.

There are three ways you can go about saving your molly fry:

1.  Installing a Breeding Box

The easiest way to save molly fry from being eaten by adult fish is to set up a breeding box in the main aquarium.

I say this is the easiest method, because you don’t have to set up a separate tank just yet and you don’t have to worry about matching tank conditions.

2.  Setting Up a Separate Tank

Setting up a separate tank, however, is a compulsory step once you need to move the fry into a rearing tank and care for them separately.

Therefore, you can start by setting up the tank either way, place the pregnant molly fish into it and remove her after she’s given birth.

Make sure to match the water conditions of the origin tank in terms of temperature, pH, and hardness.

3.  Having Lots of Live Plants

The third way of saving molly fry is something that you already must have set up in your aquarium and that’s lots of live plants and hiding spaces.

If you didn’t intend your molly fish to breed or you didn’t know that you have pregnant molly fish, you may leave the fry in with the adult fish.

This way the strongest fry will survive by hiding in the plants until they’re big enough to no longer pass for a tasty snack. In about 2 weeks’ time, they’ll be large enough to no longer be in danger of getting eaten.

What to Feed Baby Molly Fish?

Raising baby molly fish isn’t difficult either. They have a good appetite, however, the opening of their mouths is small, so you must feed them foods that fit into their mouths.

Baby mollies have a short digestive cycle, which means they should be fed often (3-5 times a day) in small portions throughout the day.

Baby molly fish eat baby brine shrimp, vinegar eels, micro worms, baby fish food, high quality flake foods crushed into a powder, etc.

Aim for variety and a balanced diet. While they like to eat often, be careful not to overfeed them. Overfeeding will foul the water and baby mollies are sensitive to toxins in the water.

Conclusion

Now that you know a few things about breeding molly fish and spotting the signs of molly fish pregnancy, you can try your hand at breeding and raising molly fry.

Be prepared that you may end up with a lot of fry if you don’t take measures to control their population (e.g. limit the number of males to females).

Molly fry aren’t difficult to raise, the key is to know how to separate them effectively from adult fish, how to feed them and keep their water parameters at optimal levels.