How to Tell if Balloon Molly Fish is Pregnant?

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Mollies need no introduction, but I’ll provide one either way. These aquarium fish belong to the Poecilia genus, Poeciliidae family, which makes them cousins to guppies, swordtails, and platies.

They are a freshwater species that prefers tropical environments and enjoys warm, clean, and healthy environments.

They even resemble guppies in size and body shape, with some key differences here and there.

But this is all public and, more importantly, common knowledge.

The situation is different when Balloon mollies come into the picture. Balloon mollies are also called belly mollies or pot belly mollies due to their unusual appearance.

They generally retain the classic molly look, except for their bulgy, protruding bellies, making it seem like they are always pregnant.

Most Balloon mollies will also display a spine bent slightly inwards.

This species is the exclusive result of selective breeding, which is another way of saying it is man-made.

Balloon mollies owe their unusual look to a genetic defect that provides them with a unique appearance.

They can reproduce naturally, but there is some concern that this genetic defect makes them more susceptible to health issues and shortens their lifespan.

There is no conclusive evidence in this sense.

But if you’ve already got your Balloon mollies and wish to breed them, what should you know about their reproductive behavior and pregnancy?

Let’s have a look!

Balloon Molly Pregnant Signs

The Balloon Molly will display pregnancy signs similar to mostly all aquarium fish, no matter the species. These include:

Hiding from Males

Male mollies are typically more aggressive and territorial than other Poeciliidae species.

They compete over food, space, females, and hierarchical dominance, and Balloon males are no exception.

The difference is that the latter is more peaceful than regular mollies if by ‘more peaceful’ we understand ‘not quite as aggressive.’

They also display high energy and stubborn and hard-headed behavior. Male fish either ignore or don’t understand the females’ ‘I’m not interested’ signs.

Their sole goal is to mate, and they won’t let anything hold them back from achieving it. Not even the fact that females do whatever they can to evade and reject them.

This generally happens when the female is either not interested or has already mated and is pregnant.

The female molly will flee and hide from males consistently, which indicates that it may be pregnant.

If you notice this behavior, monitor the situation for a while. If the males are excessively pushy, you may want to act to prevent the pregnant females from experiencing high levels of stress.

This may lead to a weaker immune system and premature birth.

Growing Belly

Yes, Balloon mollies can grow their bellies even larger when pregnant. The first signs of a growing belly begin to occur within 2 months since insemination.

If you’ve already seen your mollies, mate, monitor the female in the coming weeks.

If its belly begins to grow, it’s a sign that the pregnancy is undergoing. The molly’s increased appetite will also contribute to the effect.

At that point, you might start considering setting up a breeding tank for the coming fry.

This will also help the female feel more comfortable and free of male-related stress.

Gravid Spot

The gravid spot will become visible around halfway through the pregnancy and grow with time.

The gravid spot is nothing more than the female’s eggs becoming visible through the abdomen.

You can later see the silhouette of the fry once they hatch and begin to develop inside the female molly.

The spot is located in the lower portion of the abdomen, near the fish’s cloaca. It should become more visible after the 20-day mark when the female is around a week distance from delivery.

At this point, you should even see the fry’s eyes if you look closely enough.

Increased Appetite

Balloon mollies don’t have a vastly different appetite than regular mollies. They do just fine with one or two meals per day.

Pregnant females, however, will display increased appetite, especially when nearing delivery.

After all, the pregnant female molly now eats for itself, and its coming several dozen babies.

When the female’s appetite increases, two things will happen – the female tends to eat more and more often, and she will become more aggressive.

Food competition is common in aquarium fish, especially mollies, but it typically settles on its own. Mollies have specific pecking orders to abide by, females especially.

Everybody understands their place in the hierarchy when it comes to territory, food, and other aspects.

Those that don’t understand will be quickly put in their place by a little violence.

However, pregnancy changes everything. Pregnant mollies tend to display a bit more aggression when it comes to feeding, which you should be able to notice fairly easily.

If the pregnant female’s behavior threatens the wellbeing of other tank fish, you might need to move it into a breeding tank.


Pregnant mollies will also display more aggression in general, not only when feeding.

They are more irritable and sensitive, poking at passers-by and keeping to themselves.

They’re not looking to make friends, but this is no real reason for concern. The problem arises when the pregnant female displays gratuitous violence and frequent fights.

Mollies lack the ability to inflict serious damage upon their adversaries. After all, they don’t possess teeth, stingers, tentacles, or any other defensive mechanism.

That being said, their constant pokes at other fish’s bodies and fins can cause some damage, leading to injuries.

When untreated, they may become infected, putting the fish’s life at risk.

To prevent that, I recommend monitoring your mollies’ population dynamics and removing the aggressor in case of excessive or repeated violence.

How Long are Balloon Mollies Pregnant?

Mollies gestate around 28 days, and they mate and produce fry every month. This means that the molly is pregnant her entire life.

The problem is that most people have difficulties telling whether their Balloon molly is pregnant, fat, or just normal since they already come with inflated bellies.

Another reason for confusion stems from the fact that female mollies store the males’ sperm inside their bodies, similar to guppies.

The difference is that guppies can store the male’s sperm for up to a year, whereas mollies only settle for a couple of months.

This means that the female molly may self-impregnate in case it doesn’t have any available male around.

This may add further confusion since people don’t expect their molly to get pregnant, knowing they haven’t seen a male in more than a month.

How do I Know When My Balloon Molly Will Give Birth?

Your Balloon molly will display several signs when the labor approaches.

These include:

  • Different belly shapes – Pregnant Balloon mollies are no different than regular pregnant mollies. They both have rounded bulgy bellies. This changes for the Balloon molly when nearing labor since its belly becomes rather square than round. This is due to the developing fry taking all the space and causing contractions, changing the shape of the womb.
  • Reduced appetite – Balloon mollies will eat less and even refuse food when labor approaches. Just make sure you rule out other reasons for a lack of appetite, like disease, fish stress, or poor water conditions.
  • Increased aggression – Pregnant Balloon mollies may become more aggressive when the labor closes in. This is due to their instinctual drive to protect the fry from other adult fish. This is rather ironic knowing that mollies, like all Poeciliidae, display no maternal instincts whatsoever once the fry are born.
  • Hiding behavior – The Balloon molly will look for hiding spots towards the end of their pregnancy. You may see the female spending more time between plants, near the tank’s substrate, underwood, and hidden inside various aquatic decorations.
  • Static swimming and convulsions – Once the labor has set, you will notice your female experiencing contractions. These will manifest via rapid body movements like the fish is shaking. Prior to that, the Balloon molly will swim gently in place, refusing to move from its chosen spot.
  • Gathering near the heater – The pregnant female may need additional heating when getting ready to deliver. As such, you might see your Balloon molly spending more time near the heater, where the water is warmer.

As the labor approaches, the Balloon molly female will typically display all these symptoms in succession.

This is the cue you need to provide your female molly with the necessary setting to deliver the fry in peace.

How Many Babies do Balloon Molly Fish Have?

Mollies will deliver around 20 to 60 fry, depending on a variety of factors.

These may be environmental, like temperature, dietary, the fish’s age, and the number of its pregnancy.

Older mollies who have already gone through several pregnancies may deliver closer to 60 fry than younger, more inexperienced ones.

Whatever the case may be, move the female into a breeding tank if you want to keep your fry.

Otherwise, their chances of survival in the main tank are slim to none. This is mainly due to the fry’s behavior upon birth.

Molly fry tend to congregate at the water’s surface, making them visible to other fish who will take them for prey.

All tank occupants, mollies included, will feed on the fry shortly after they’re born.

Setting up a breeding tank will allow the fry to grow in a safe and comfortable environment without having to fear for their lives.

Just make sure you set up the tank temperature higher than that of the main tank. Your fry also require optimal tank conditions and high-protein food 2-3 times per day during their first 2-3 weeks of life.


Balloon mollies make for an exotic aquarium option. Don’t be intimidated by their unusual appearance; they abide by the same rules as all mollies.

They don’t require special treatment, display the same molly-specific behavior, and are as easy to care for as any other Poeciliidae.

If anything, Balloon mollies are even easier to care for than the regular ones, since they tend to be friendlier and calmer in general.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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