How to Tell If a Molly Fish is Pregnant {4 Sure Signs}

Do you have a female molly fish in your tank or pond? Are you wondering how to tell if a molly fish is pregnant?

Unlike most fish, mollies are livebearers, meaning they give birth to their young ones alive. What are some tips to save Molly fry?

This article will fully explain the sure signs to tell if a molly fish is pregnant.

How to Tell If a Molly Fish is Pregnant

When a molly is pregnant, you will notice some physical changes:

  • like protruded stomach
  • having a dark triangular spot near the anal vent
  • behavioral changes
  • sluggish swimming

The pregnant female molly will stay away from other fish in the water and move slowly.

Signs Your Molly is Pregnant

Your molly is not human, so you should not expect it to walk up to you and tell you it’s pregnant. However, you have to look out for changes, both behavioral and physical changes, before you can tell if it is pregnant. These signs will give you enough knowledge of the condition of your fish.

If you want to tell if your molly is pregnant, you have to look out for two kinds of signs:

  • behavioral 
  • physical signs

Behavioral signs include activities and reactions to its environment, while the physical signs entail its body change and appearance.

Ways to Tell If A Fish Is Pregnant

1. Slow movement

This sign is a common behavioral sign that tells your fish is pregnant. You will notice the molly swimming slowly in the water. You have to be sure of this sign as it can also be a symptom of diseases and illness.

2. Seclusion

You will also notice the female molly secluding herself from other fish in the water. This behavioral sign is obvious as you will see the fish move far away from other fish, resting and looking for calm and cool locations.

3. Protruded Stomach

This sign is a common physical sign in most pregnant fish. You will see your molly’s stomach becoming bigger as the babies mature in her. You will notice her stomach stretching out and becoming bigger.

4. Dark spot

You will also notice the appearance of dark spots near her anal vent. The triangular dark spot becomes darker and more obvious as the pregnancy approaches the ripe stage.

Once you start noticing these signs, you should start preparing for her fries’ arrival. You have to ensure she gets adequate requirements and conditions.

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Molly Pregnancy Stages

Did you know that Molly fish can be pregnant for up to 70 days?. There are different stages that a pregnant molly fish goes through including:

  1. insemination
  2. egg development
  3. birthing

1. Insemination

During the insemination, a molly which is a livebearer can carry the fry inside her body. The fertilization of the eggs take place inside her body. The gonopodium of a male molly is inserted into the female’s anal vent and the sperm is released this way.

2. Egg Development

After insemination with the eggs fertilized within the body, they begin to grow and develop eggs inside the pregnant molly. This is the gestation period that can last from three to six weeks. The belly will swell and  she will grow in girth.

3. Birthing

It’s time for your pregnant molly fish to give birth. The fish will come out as live free swimmers known as her fry. You will notice that these fry don’t have egg sacs attached to them.

They will require looking after from you because mollies do not look after their fries after they give birth. You must separate the mother after she has given birth to prevent her from eating them.

What Does a Pregnant Molly Look Like?

Here are some obvious signs that a Molly is pregnant:

  • A Swollen Belly
  • A Gravid Spot Under The Belly
  • Behavior Changes
  • Eating More
  • Seeking Warmth

At first you will notice a swollen belly. This is one of the easiest ways to see if a fish is pregnant or not. Also look for the gravid spot under the belly. It is a dark triangular mark underneath the anal cavity. This is where the baby fry are inside her.

She could be carrying up to 120 babies at one time. You may also notice behavioral changes like becoming more aggressive to other tankmates.

She will like to be left alone in and will seek to avoid others. Make sure she has plenty of hiding places. At this time, she will probably eat more as well. A pregnant molly may also hover near the heating system of your tank to seek warmth.

How Long Are Molly Fish Pregnant For?

Mollies are one of the few fish that give birth to their young ones alive. They can carry their young ones for about 6 to 10 weeks, i.e.

  • Mollies can be pregnant for six to ten weeks.
  • Mollies are a type of guppy as they are of the same genus but different species.
  • Mollies can carry 20 to 100 young ones during pregnancy and give birth.
  1. They also breed frequently, making them discharge as many offspring much as they can.
  2. You also have to provide adequate water and tank conditions to ensure her good health.
  3. Sometimes, it is best to remove the expectant mother and keep her separately in another tank for special attention and safety.

How to Tell If your Molly Fish is about to Give Birth

When your molly fish is about to give birth, you will notice the stomach to be unmistakably large.

  1. The babies in her are now larger and more ready to see the world, causing her stomach to expand to accommodate their growing size. Her stomach’s size will show how much she is ready to let her babies out.
  2. You will also start to see her gravid becoming more obvious. The dark triangular spot near her anal vent becomes much larger and darker than before. In addition to this, the molly’s peritoneal wall begins to stretch, causing the dark spot to stretch and increase.
  3. You will also notice the eyes of the fry becoming visible. It is not always visible, but you will sometimes see the young ones’ eyes through the thin walls of the molly’s gravid spot. You can also notice the fry’s body from the walls of her stomach.
  4. Your molly will also develop a bulge below her gills as the delivery date becomes nearer. You will also notice your molly’s outline becoming fairly square. She starts finding it difficult to swim around in the water at this stage.
  5. When you start seeing these signs, you should remove your pregnant molly from the tank and place her in another. It will save her and her fries from impending danger from other fish and other factors. It will also enable you to pay special attention to the female molly and her fries.
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How Mollies Act Before Giving Birth

Your molly fish will show you signs that it wants to give birth. It is now left to you to notice these signs and take necessary actions. Your molly will keep showing signs, even till the last minute before its delivery.

Mollies can sometimes:

  • act funny when they are about to give birth
  • start acting restless
  • try getting a comfortable position in the tank
  • secluding themselves from other fish in the tank 
  • leave their tankmates and settle in a calmer and cooler water location.
  • prepare places in the tank for their new kids’ arrival.

The molly can also show a bit of aggressiveness when ready to give birth. You will also notice she does not swim much. She will stick to a position for a longer time than she normally does.

How Long Does it Take for a Molly to Give birth?

Molly will give birth right after they complete their gestation period. The gestation period in molly fish can last about 6 to 10 weeks. In rare cases, the gestation period may exceed ten weeks, most unlikely to occur.

After the gestation period elapses, the molly will give birth to her young ones. Before a molly can go into gestation, she has to become mature.

Furthermore, male mollies will become matured and ready for reproduction when they reach 12 months.

Female Molly Development

Female mollies usually attain maturity at half the age of males, so they will be ready for pregnancy when they reach six months. So, it will take about nine months for your molly to give birth. This nine-month count starts from her birth.

Mollies can carry about 20 to 100 fries in them during pregnancy. They also breed more frequently, making them suitable for you to keep for breeding purposes.

In addition to this, mollies will breed as soon as their young ones become mature, continuing the reproduction cycle repeatedly.

Do Mollies Eat Their Babies?

Like many livebearers, cannibalism is normal with mollies. They tend to eat smaller and weaker fish, regardless of the species. Mollies will definitely eat their babies when they get the chance.

Mollies do not lay eggs but give birth to their young ones alive. However, when mollies give birth to their young, the small fish are usually weak and fragile, making them prone to attack from other fish and even their mothers.

  • You might also need to take the necessary actions if you want to keep your small mollies alive and safe.
  • You might need to remove the fries and keep them in another tank for their safety.
  • You will also need to cater to them separately to ensure their well-being.

Tips to Save Molly Fry

You need to save your molly fry from adult mollies and other fish in the tank. If you do not protect them, you might lose them to other fish in the tank as food. Here are some simple tips for you to save your molly fry;

1. Set up a separate tank

One of the best ways to save your molly fry is to set up a separate tank for them. Setting up a separate tank will help you keep out fish that will eat your molly fry. It will also enable you to provide the needed and adequate requirements.

2. Set up a breeding box

One of the easiest ways of keeping your molly fry safe is to set up a breeding box in the main tank. It will save you the stress of setting up a separate tank for them. The breeding box will provide the molly fry with what they need and save them from other fish.

3. Add plants and structures

If you do not have the means to set a separate tank or use a breeding box, you have much work. You will need to add plants and structures to the tank to create a hiding space. Although this might not be very effective, it will do a good job of saving them.

4. Set up filter system

Molly fry are small and fragile, so you need to provide them with what they need. You have to set up a filter system for them. The filter system will ensure they have a healthy and safe aquatic environment.

5. Feed them adequately

Food is necessary for your molly fry. You have to make sure you give them the right food and at the right time.

How Long Do I Need to Separate My Baby Mollies?

You have to separate your baby mollies from the main aquarium until they are large enough not to fit into the mouth of other fish.

  • You can keep the mollies in a separate tank for about 4 to 6 weeks.
  • By this time, the baby mollies should have grown large enough for the adult tank.

You have to be sure the adult mollies will not be able to eat the baby mollies before adding them to the tank.

In addition to this, if you are using a breeder, you will also have to be sure they are of the right size before returning them to the tank. When the fish are about eight weeks old, they will fit the adult tank.

What to Feed Baby Molly Fish?

Your baby molly fish needs to eat for it to grow into the adult stage. You have to make sure you feed it with the right food to ensure its growth and development. One of the foods you can give your molly baby fish is fish flakes.

Baby molly fish will eat fish flakes when you give them to them. You have to make sure you crush the flakes into a fine texture for the fish to eat them easily.

  • Crushed fish flakes will provide your baby fish with the needed nutrients.
  • You can also feed them baby brine shrimps.

Your baby molly fish will eat baby brine shrimps as long as they can fit into its mouth. Brine shrimps are highly nutritious and beneficial to baby molly fish.

  • Feed them with little plants and algae to aid their rapid growth and development.

Your baby mollies will grow as much as you feed them. If you feed your baby mollies well, they will be of large sizes in eight weeks.

You will even be able to add them to the large tank by then. The baby mollies will be large enough to eat the same food as other adult mollies. They will also be free and safe from attack from adult mollies and other fish.


You can tell if your molly is pregnant by looking out for some signs she will exhibit.

When your molly is pregnant, it will definitely exhibit obvious behavioral and physical changes.

When you notice these signs, you should know your molly is full of babies.


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John Brandon

John has kept fish all his life (since he was about 5). He started with keeping guppies and fell in love with fish keeping almost straight away. That was 40 odd years ago. These days John still keeps fish and currently has two large tanks where he keeps many different types of fish such as Angelfish, Neon Tetras, Goldfish, Guppies and many more.