5 Ways To Tell If Your Molly Fish Is Pregnant

Last Updated on 2024-06-13

If you keep male and female molly fish in your aquarium at home, you’ll need to know how to tell when your female mollies are pregnant. In this article, you’ll find out 5 ways to tell if your molly fish is pregnant, how long they stay pregnant, how to tell when they’re about to give birth, and how to take care of them!

So keep reading to find out everything you need to know!

Key Takeaways:

  • To spot a pregnant molly fish, watch for a swollen belly, a gravid spot near the anal fin, behavioral changes like increased aggression and hiding, increased appetite, and seeking warmth.
  • Molly fish have a 50-70 day gestation period and prefer warmth during pregnancy.
  • Creating a secluded birthing environment with hiding spots is crucial for a comfortable experience.
  • Isolating a pregnant molly in a breeder tank is essential for fry safety.

So, Is Your Molly Fish Pregnant?

If you’re asking this question, then you’ve probably noticed something unusual about your molly fish and suspect she might be pregnant. Most fish owners notice a swollen belly and some behavioral changes in the early stages. 

Fortunately there are several easy to tell signs that your molly fish is pregnant.

If you think your molly fish is pregnant look for the tell-tale signs such as a gravid spot behind the anal fin, a swollen belly, eating more, seeking warmth, hiding, and becoming more aggressive towards other fish. These signs in combination with each other are clear indicators of pregnancy.

You’ll need to take extra care if your molly is pregnant, especially if you want to keep the babies . Fully grown mollies are known to eat their offspring, so make sure you move your molly to a fry tank before she gives birth, so you can remove her after.

If you think your molly is pregnant, here is a more in-depth look into the signs you should be looking for.

How To Tell If A Molly Fish Is Pregnant

There are several ways to identify a pregnant molly. Some are more obvious than others, but if you know what to look for, you’ll soon pick up on the behavioral and physical changes your Molly goes through throughout her pregnancy. 

1) A Swollen and Stretched Out Belly

One of the most obvious signs that your Molly is pregnant is if she is looking a bit more chubby around her abdomen area than usual. You’ll notice rounding when she is close to giving birth. Remember if you want to keep the babies move your molly to a separate tank to allow her to give birth in peace and to protect her babies.  

Mollies usually have a significantly rounded belly, given that they can carry up to 40-100 babies at a time. Although the fries are absolutely tiny, it’s still a large number of babies to fit into a Molly’s small body. The more babies she is carrying, the rounder her belly will be. 

2) A Gravid Spot Under Their Belly

You may also think that your Molly is simply a bit plump from eating too much. The easiest way to tell that they are pregnant and not just fat is to keep an eye out for a dark spot that will appear towards her anal cavity. 

As your fry grow and grow, the gravid spot will start to get bigger, in fact, near the end, you may even begin to see the fry through the gravid spot.

But of course, if you have black mollies, you probably won’t notice this. The more light and colorful a molly is, the more obvious the darker section on their belly will be.

3) Their Behavior Changes

Another giveaway is that your Molly fish will become more aggressive towards other fish if bothered. They won’t actively attack them, but they’ll try to avoid them as much as possible. To keep a molly fish happy, you should ensure there are plenty of hiding spots in the tank. 

A pregnant molly will often hide away so that she feels safe and does not become bothered by other fish in the aquarium. This is one of the signs that can appear as early as seven days after conception. 

4) A Pregnant Molly Fish Will Eat More

Pregnant Mollies will eat more because they also have to provide food for the fry they are carrying. If you notice that your molly fish are eating more than they usually do, it could be because they are pregnant. 

5) They Seek Warmth

Lastly, if you notice your Molly hovering closer to the tank’s heating system or temperature stabilizer, this may also be a sign that she is pregnant. Mollies will seek a heat source so that they remain at a constant temperature throughout their gestation period. 

For the same reason, you may also see your mollies hovering closer to the surface, especially if your tank uses an overhead UV light. The light bulb will emit heat, even through the water’s surface, thus making an ideal environment for mollies to hang around in when they are pregnant. 

Swollen BellyA rounded abdomen, especially close to giving birth.
Gravid SpotA dark spot near the anal cavity that grows as the fry develop.
Behavioral ChangesIncreased aggression, hiding, and seeking solitude.
Increased AppetiteEating more than usual to nourish the developing fry.
Seeking WarmthHovering near the tank’s heating system or temperature stabilizer.
beautiful molly fish in aquarium

How Long Does a Molly Fish Stay Pregnant?

Molly fish have an average gestation period of 50-70 days. However, this heavily depends on which variety of Molly you have. And also in some cases the conditions in the tank as well.

Mollies also have the ability to keep the male’s sperm inside them for months at a time, therefore fertilizing their eggs at time intervals. Which means they could actually be pregnant consistently over a longer term. 

Whether or not they give birth is dependent on the environment they are in and whether or not they feel comfortable. As mentioned, mollies need to be warm and in a safe, concealed environment. Many breeders will separate pregnant mollies from the main tank to ensure they give birth in peace.

Here are the stages of pregnancy that a molly goes through once her eggs have been internally fertilized. This will make it easier for you to know how long she has before she gives birth. 

Stage 1: Conception

If you have male and female mollies in the tank, they may mate often. A female molly can keep sperm inside her and fertilize her eggs every 30 days. At some point during the first stage however, conception will occur.

Stage 2: The Formation of the Embryo

After an egg has been fertilized, an embryo will begin to form in each of the egg cells. You can physically see this is happening by observing the gravid spot we mentioned above. This usually appears around 7 days after conception. 

This is the stage in which you may begin to notice your pregnant molly begin to start eating more.

Stage 3: The Fry Develop

Each of the eggs has the perfect conditions for a molly embryo to develop into a fry. As they grow, you will notice the pregnant Molly’s belly grow and grow. This is going to be the bulk of the time your molly is pregnant.

Stage 4: The Pre-birthing Stage

This is the stage a molly fish is getting ready to give birth. The fry will be fully developed as they reach the end of their time in their mother’s belly. In some cases you may even see the fries’ eyes inside the Molly at this stage. 

Stage 5: Birthing Molly Fries

Lastly, your molly will give birth to her fry who already know how to swim At this stage they can give birth to up to 100 fry!

Just remember, that the fry aren’t safe from the mother. Once she’s birthed the she’ll feel no loyalty towards them and she won’t be afraid to eat them.

ConceptionMating occurs, and the female can keep sperm for up to 30 days.
Formation of the EmbryoA gravid spot appears around 7 days after conception.
Fry DevelopmentThe belly grows as the fry develop.
Pre-birthingThe fry are fully developed, and you may see their eyes.
BirthingUp to 100 fry can be born.

How To Tell If Your Molly Fish Is About to Give Birth

It’s important to know when your Molly is about to give birth so that you can provide the best possible environment for her when she does. Here are the top signs to look out for so that you can prepare the molly mother for birth. 

The Gravid Spot Is Very Visible

The dark spot under the Molly’s belly will now be at its most visible point. The spot is triangular in shape and gets darker and larger the closer a molly is to giving birth.

The spot is located towards the anal vent of the pregnant Molly. 

Mollies Will Try to Hide in the Tank

A heavily pregnant molly will try to hide in the tank so that she can give birth in peace. She will not want to be disturbed by other fish in the tank. Plants and shells that may be in the tank will serve as great birthing spots for a molly.

However, if you want to keep the fry you should move her to a new tank altogether.

They‘ll stop eating

If you notice a loss of appetite in a female molly, she is likely ready to give birth. Fish swim to the surface when you give them food. If a molly holds back, this is a sign that she is ready to release her fries.  

A Rounded Area Develops Under Their Gills

Aside from a rounded belly, an area underneath their gills will also become rounded. This means that the “womb” has reached its full capacity. The molly fish will want to give birth as soon as possible to alleviate any strain this has on her body. 

You Can See the Babies’ Eyes

As the embryos become more and more developed, you can start to distinguish the individual fries by observing their eyes. When the fry’s eyes become the most obvious, it won’t be long before the mother molly gives birth. 

How to Take Care of Pregnant Molly Fish

As we said, a pregnant molly will be happier in the right environment. Here are some tips on how to take the best care of your Molly throughout her pregnancy. 

Make Sure A Pregnant Molly Has a Warm Environment

Mollies will actively look for a heat source to regulate their body temperatures. If you want to make sure your Molly is completely at ease, you should make sure the tank is warmer than usually at around 78-81°F

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Separate Her From The Main Tank

Removing a pregnant molly from the main tank will allow her to give birth in a safe environment for the fry. It will also prevent other fish from bothering the Molly.

Mollies tend to look for quiet spaces anyway, so giving her what she wants will make for the most comfortable birthing experience possible. 

Pawfly Aquarium Fish Breeding Box Acrylic Hatchery Incubator Tank with Suction Cups Small Isolation Box for Baby Small Fish Shrimp and Betta
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Provide Hiding Spaces For Your Molly

Make sure your tank has lots of plants and hiding paces. Mollies will appreciate extra places in the tank to hide. Once a molly feels safe and secluded enough, she will give birth. 

(Check out the 33 best aquarium plants for beginners!)


Here are some frequently asked questions that people have about their molly fish giving birth!

How Do You Know if Your Fish Is Bloated or Pregnant?

The easiest way to tell if your molly is pregnant not bloated is to look for a gravid spot. This is the dark spot that appears under the fish’s belly, near the anal fin. 

How Many Babies Do Mollies Have?

Mollies typically give birth to between 20 and 100 fries. This heavily depends on the type of Molly you have. Some mollies have been known to give birth to up to 120 babies. 

Do Mollies Give Birth at Night?

A lot of mollies will give birth at night so the fry have the best possible chance of survival, especially if they are in a tank with other fish. Mollies will sometimes give birth during the day if in a dark environment. 


If you suspect your molly fish might be pregnant, there are several signs you can look out for. A swollen belly and a gravid spot are the most obvious giveaways.

There are also some behavioral changes you may notice such as aggression towards other fish, seclusion from other tank mates, and an increase or decrease in appetite, depending on their pregnancy stage.

And lastly, you need to make sure you know when your molly is going to give birth to ensure that you move them to a breeder tank to make sure the fry are safe.

If you liked this article, make sure you check out the rest of the website! Otherwise, have a great day!

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