5 Ways To Tell If Your Molly Fish Is Pregnant

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. Mollies will naturally breed often if there are both genders of fish present in the tank.

Molly fish are a beautiful addition to your aquarium. They come in quite a few varieties and are full of character. Molly’s also have a naturally prominent belly, so many wonders have problems identifying whether or not they are pregnant.


This guide will help you understand what signs to look for to identify whether or not your Molly fish is pregnant successfully. Once you can identify and read any sign of pregnancy, this will allow you to make the right decisions to rear healthy Molly babies. 

So, Is Your Molly Fish Pregnant?

If you’re asking this question, 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. 

There are several easy to tell that your molly fish is pregnant. You’ll need to take extra care if this is the case, especially if you want to keep the babies your Molly produces. Fully grown mollies are known to eat their offspring, so you’ll need to keep an eye to know when the Molly is about to give birth. 

Molly fish give birth to live young, which places them in the category of livebearers. We usually assume that all fish lay eggs, which become separately fertilized by the male fish. In the case of mollies, males and females mate, causing the female to become pregnant. 

The gestation term of a molly fish can last between 20 and 40 days. With such as short time period in which a molly is pregnant, they often produce young. If you don’t know your molly fish is pregnant, you’ll probably get a pleasant little surprise every now and again when you see the tiny fry swimming around the tank. 

Do you think your molly fish might be pregnant? Please keep reading to find out some helpful tips and tricks on how to know and how to care for a pregnant molly fish and her fry. 

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. It’s necessary to move the 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 120 babies at a time. Although the fries are absolutely tiny, it’s still a large number of babies to fit into the 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 triangular mark that will appear towards their anal cavity. 

This dark mark is the cluster of baby fry inside her, which you’ll be able to see even better under the UV light of your fish tank. As the fry develops, you will notice their eyes most prominently. The eyes are the largest part of the fry’s body. 

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. The dark mark that appears is known as a gravid spot. 

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

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. 

Molly fish

How Long Does a Molly Fish Stay Pregnant?

Molly fish have an average gestation period of between 20 to 40 days. However, this heavily depends on which variety of Molly you have. For example, dalmatian mollies can stay pregnant for up to 70 days before giving birth. 

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. They usually fertilize their eggs every 30 days, 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. 

We’ve listed 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. 

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. 

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. 

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. You will see the fries’ eyes inside the Molly at this stage of the pregnancy. 

Stage 5: Birthing Molly Fries

A molly then releases her fries which will already know how to swim. Mollies will give birth to up to 120 babies at this stage. 

Mollys are livebearers, which means that they don’t lay eggs, but instead give birth to live young. Mollys can give birth to as many as 120 fries at a time. Unfortunately, it is in mollies’ nature to eat their babies shortly after they are 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 fr 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. Some breeders separate them entirely. 

They Don’t Eat

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 between 23 to 29 degrees celsius. 

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. 

Provide Hiding Spaces For Your Molly

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

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

Your fish could just be getting fat due to eating too much. However, if they are pregnant, they will develop a gravid spot. This is the dark spot that appears under the fish’s belly. 

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?

Most of the time, Mollies will give birth at night. This is so that the fries 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. Mainly, a swollen belly and a gravid spot are the most obvious giveaways. We have also listed some behavioral changes to keep an eye on. 

These include aggression towards other fish, seclusion from other tank mates, and an increase or decrease in appetite, depending on their pregnancy stage. You need to make sure you know when your moly is going to give birth to avoid any surprises and to protect the babies.  

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