How to Care for a Pregnant Molly Fish?

Molly fish are a popular addition to many aquariums due to their peaceful nature and vibrant colors. 

These live-bearing fish give birth to live young, making the pregnancy and birth process an exciting and unique experience for aquarium enthusiasts. 

It’s important to provide a healthy and stress-free environment for pregnant molly fish, as well as monitor their diet and prepare for the arrival of the fry. 

In this guide, we’ll explore everything you need to know about the pregnancy process in molly fish, including signs of pregnancy, caring for pregnant molly fish, and ensuring a successful birth for the fry.

How Can You Tell if a Molly Fish Is Pregnant?

How Can You Tell if a Molly Fish Is Pregnant

As livebearers, mollies give birth to live fry, making it essential to know when your female molly fish is pregnant. 

In this section, we will discuss the signs that indicate a pregnant molly fish and what to expect during this period.

Swollen Abdomen

One of the first and most apparent signs of a pregnant molly is a swollen abdomen. 

As the fry inside her belly grows, her abdomen will expand, and her overall body shape will change.

However, it’s important not to confuse a swollen abdomen with overfeeding or constipation

Keep an eye on the gradual increase in size, which is an indicator of pregnancy.

Behavioral Changes

A pregnant molly may exhibit behavioral changes, such as increased aggression or hiding. 

These changes are a result of her attempt to protect her unborn fry and find a secure place to give birth. 

You may notice your pregnant molly seeking shelter among aquarium decorations or plants more frequently and staying away from other fish in the tank.

Increased Appetite

Another sign that your molly fish is pregnant is an increased appetite. 

As the fry develops inside her belly, she requires more nutrients and energy to support their growth. 

You might observe her eating more than usual or showing an increased interest in food during feeding times.

Gravid Spot Under the Belly

A gravid spot is a dark-colored area on the lower part of a female molly’s belly, close to the anal vent. 

This spot becomes darker and more apparent as the fry develops and becomes visible through her skin. 

Light-colored mollies are more likely to show this sign, making it easier to confirm pregnancy in these cases.

How Long Does a Molly Fish Stay Pregnant?

The pregnancy period for a molly fish typically lasts around 50 to 70 days. However, this can vary depending on factors such as water temperature, diet, and genetics. 

During this time, the female molly fish will carry the developing embryos inside her body until they are fully formed and ready to be born. 

Take a look at all stages of molly fish pregnancy so you know what to expect when your fish is expecting:


Molly fish have a gestation period of around 50 to 70 days, and the process begins with conception. 

Female mollies can store sperm for months, so they may fertilize eggs as often as every 30 days, even without a male present in the tank.

Formation of the Embryo

After successful fertilization, the embryo starts to form inside the pregnant molly fish. 

This process may last several days, and during this time, the mother’s abdomen will start to noticeably swell.

Development of the Fry

Throughout the pregnancy, the fry will develop and grow inside the female molly. 

The number of fry can vary greatly, ranging from 10 to 100, which depends on the species and maturity of the mother. 

As the fry continues to develop, you will notice the female getting larger and her gravid spot darkening.

Pre-birthing Stage

In the days leading up to the birthing, your pregnant molly fish will show signs of giving birth soon. 

She will likely become less active and seek out darker spots in the tank. 

Be sure to provide plenty of hiding spots and maintain water conditions between 70 to 82°F (21 to 27.7°C) to keep the pregnant molly comfortable.


When it’s time for the molly fish to give birth, the birthing process typically lasts up to a few hours. 

Depending on the species, a molly fish may lay anywhere from 10 to 100 fry. 

After the fry is born, neither parent provides care, so you should consider separating the fry from the adults to ensure their safety.

By understanding the entire process, from conception to birthing, you can better care for your pregnant molly fish and support her throughout her pregnancy.

Caring for Pregnant Molly Fish

Caring for Pregnant Molly Fish

Caring for pregnant molly fish is an important and rewarding part of aquarium keeping. 

Here are some tips for ensuring a healthy pregnancy and birth for your molly fish:

1. Separate the Pregnant Molly

When caring for a pregnant molly fish, it’s essential to move her to a separate tank to keep her comfortable and reduce stress from other fish. 

This will also ensure the safety of the embryos and provide a controlled environment for monitoring water parameters, temperature, and diet.

2. Provide a Warm Environment

Molly fish, including black mollies and Dalmatian mollies, thrive in warm water temperatures. 

To ensure the health of the pregnant molly, maintain a water temperature between 78-82°F (25-28°C) using a reliable heater. This heater is highly recommended and available on Amazon.

Additionally, it’s vital to monitor water parameters like pH, which should be kept within a range of 7.0-7.8.

3. Provide Hiding Spaces

Pregnant molly fish tend to spend more time hiding and require a secure environment. 

To accommodate this behavior, provide hiding spaces like caves, plants, and decorations. 

Keep an eye on her appetite, as an increased appetite indicates a need for more nutrients during pregnancy. 

It’s essential to perform regular water changes to maintain optimal water quality and ensure proper embryo development.

How to Tell if a Pregnant Molly Is About to Give Birth?

One of the most obvious indicators that a pregnant molly is about to give birth is the appearance of a square, distended stomach, and a darker, opaque gravid spot. 

You might also notice your molly’s appetite diminishes and hiding behind decorations or plants becomes more frequent.

Another sign to pay attention to is your molly’s swimming pattern. 

Pregnant mollies approaching delivery tend to stay in one place longer than usual, and may even shiver while swimming. 

Lastly, a pregnant molly about to give birth might exhibit some aggressive tendencies and isolate herself from other fish.

By attentively monitoring your pregnant molly’s behavior and appearance, you can ensure that you’re prepared to support her when the time comes for her to deliver her life young.

FAQs About Pregnant Molly Fish

How Long Is a Molly Fish Pregnant For?

Molly fish have a pregnancy duration of around 60 days. 

However, this can vary depending on factors like water temperature and stress levels. 

Make sure to maintain optimal conditions to keep your pregnant molly fish comfortable and healthy.

How Long Do Mollies Give Birth For?

The birthing process for mollies can vary depending on the size of the female and the number of fry she is carrying. 

Typically, the birthing process can take anywhere from a few hours to a full day. 

During this time, the female molly fish will release the fry from her body, and they will swim to the surface of the tank. 

What Do I Do With My Pregnant Molly?

If you have a pregnant molly fish in your aquarium, it’s important to provide proper care to ensure a healthy pregnancy and birth. 

This includes providing a stress-free environment by avoiding sudden changes in water conditions or tankmates and providing plenty of hiding places and plants for the fish to feel secure. 

Monitoring water quality is also essential for the health of both the mother and her fry, so regularly test the water for ammonia, nitrite, and nitrate levels. Perform water changes as needed to keep the levels within safe parameters. 

A nutritious and varied diet is also important for pregnant molly fish to support the development of their embryos, so offer a mix of high-quality flakes, pellets, and frozen or live foods such as brine shrimp or daphnia.