Pregnant Molly with Babies – What You Should Know?

Mollies are actually one of the most popular and loved fish species among aquamarine enthusiasts. Mollies do not lay eggs and are an ideal choice of live-bearing fish to place in a fish tank.

How do mollies breed? Mollies give birth to live babies. They are very easy to breed for the most part, and a single female mollyfish can produce over a hundred baby mollies at one time. 

Pregnant Molly Fish? Babies? What to Do (Video)

This article will help you care for your pregnant molly and its fry and will take you through all the stages of molly’s pregnancy.

How to Know if Your Molly is Pregnant?

Once your fish have attempted breeding, you will obviously be curious to know if the breeding attempt was successful or not.

Firstly, you must closely observe the female molly and keep an eye on its everyday behavior. If your brightly-colored molly is pregnant, you will begin to see a black line on its lower belly.

This will be a little hard to notice if you have black mollies. Another thing that might help you out is that the belly of the mollyfish will appear swollen. Keep a close eye on them and mark your calendar when you see signs of pregnancy.

The gestational period for a mollyfish is around 60 days. These would roll by very quickly. So being on top of their schedule is important.

Another tricky aspect is that the female mollies have the ability to store sperm for months and can fertilize eggs as often as every 30 days. So even if your fish tank has no males, the female molly might end up pregnant. Mollies mostly release approximately 10 to 60 live fish at once.

Keep an eye out for the following signs of mollyfish pregnancy:

  • Black line on the belly
  • Swollen belly
  • Black spot near the anal vent
  • Behavior changes, such as staying isolated and eating more.

Pregnant Molly Fish 101

Mollyfish Give Birth to Live Fish

Mollies have livebearers characteristics, like Guppies, Platy, and Swordtails. These kinds of fish do not lay eggs. This unique feature makes them an excellent choice for fishkeepers looking to witness the fascinating process of live birth in their aquarium.

If you intend to raise molly fry into adults, you’ll need to consider a few options to prevent the female molly from consuming the newborn fry.

One option is to keep a breeding box in your fish tank. This will isolate the mother fish from her fry and keep her within the box.

You can also keep a close eye on the pregnant molly and move her into a separate tank as soon as it gives birth. If you do not want to overpopulate your tank, let nature do its bidding and see how many molly babies survive.

If your fish tank is full of hiding spaces and has a cover, then there is a pretty good chance that the fry will survive. All you need to do is provide them with ample plants and pieces of wood to hide and a clean healthy environment.

Pregnant Molly Fish Behavior

Mollies are not the most aggressive fish species, but the behavior of the female mollyfish changes during the length of its pregnancy. When mollies become pregnant, they exhibit aggressive behavior, which is quite different from their usual demeanor.

They also like to hang around close to the heater to stay warm. They begin to hide more and are always alert to their surroundings.

Taking Care of Molly Babies

Once the mollyfish gives birth, you can ensure the long-term health and safety of the baby mollies by:

  • Providing them with a safe environment
  • Feeding them regularly
  • Conducting frequent water changes
  • Acclimating the fry to your fish tank

Equip a Nursery Tank

Before the pregnant female molly gives birth, it’s crucial to have a properly set up nursery tank ready. This tank should ideally have a capacity of five to twenty gallons, depending on whether you plan to keep the mother with her fry or separate them. For keeping them together, a larger tank is preferred, while a 10-gallon tank is suitable for separating the fry from the mother.

Add a Filter to the Tank

Setting up a filtration system in your tank is very important, especially for your fry. You can choose a simple sponge filter or any other appropriate filtration for the size of your tank. If you do not want to use a mesh or foam-covered filter, then purchase a fitting or attachment from any pet store in order to make the fish tank safer for the fry.

Another option is to make your own filter modification. Try stretching a small strip of nylon, place it on top of the filter, and fasten it with a rubber band. It is vital that your filter is safe, or there is a chance that your fry will get sucked up.

Place Plants

Adding plants to your fish tank is also necessary in order to provide your fry with shelter and ample hiding spots. You can use both natural and artificial plants, but artificial ones are more suitable as they do not cause an unnecessary mess.

Try placing plants in the tank that float so that the fry has an area near the surface of the water to hide under immediately after they come into the world. Broad-leafed plants like Java ferns and grasses are some good options to put in your nursery fish tank.

Heat the Nursery Tank

Mollies are tropical fish, and water that is in line with the tropical climate is necessary for their well-being. Try keeping the temperature of your water between 72 and 84 degrees Fahrenheit by making use of an aquarium heater.

Do some research on which heater will be most suitable for your tank. You may need about 5 watts for every gallon of water in your fish tank. Another thing you should do is monitor the temperature of your fish tank by using an aquarium thermometer.

Adding a Breeding Trap

If you are unable to find a breeding tank, then you can use a mesh breeding tank. You can easily purchase the mesh breeding boxes, which protect small fish from any pet store. Hang it at the side of your aquarium. Remember to sterilize the mesh by using warm water in order to provide the fry with a clean environment.

The most important thing you should be aware of is that the fry will outgrow the mesh box very quickly and would have to be transferred into a separate tank before they are introduced into the larger main fish tank.

Introducing the Molly Babies

If your pregnant molly seems to be close to giving birth, the first thing you should do is move the mother molly. You will easily know if the fish is about to give birth, as mentioned earlier.

A swollen belly and dark line at the underside of the molly are sure signs that your molly is pregnant. The spots near her tailfin will darken as the delivery date gets nearer. Adult mollies, especially male mollies, feed on newly born fish, so it is important to move the mother mollies to a nursery tank even before the birth of the fry.

See also  Can Platy Fish Live in Cold Water Without a Heater?

If you purchase the fry from the pet store or a breeder, then remember to pick them up as quickly as possible after birth and make sure that you carry the fry in a sealed bag filled with warm water and sufficient room for the fry to move around. Avoid taking long routes home as you want to cause as little stress as you can to the fry.

When you reach home, do not immediately empty the fry-carrying bag into your fish tank. First, let the bag sit in the fish tank water for about 15 minutes in order to bring the water temperature of the bag equal to the temperature of the fish tank. If you instantly introduce the fry into the fish tank, then some may die because of the shock.

After 15 minutes, open the bag and leave the fry all on their own. Do not squeeze the bag to push the fry out, and do not dump the bag into the water of the large fish tank.

If you want to direct your fry into the breeding tank, slowly allow the water to flow from the plastic bag to the breeding trap to prevent any fry from going into the bigger aquarium.

Keep an eye on the fry in your fish tank. Observe their behavior and make sure that they are all hiding or moving. If any of the fry did not survive, then make use of a net to remove it from the fish tank.

If the mother Molly, and the molly babies are in the same tank, then observe the mother and see whether she is showcasing any aggressive behavior towards the fry. If the mother seems tense, just move her into a separate tank.

Raising Your Fry – What You Need to Know

As soon the fry is introduced into the new tank, feed them. You can easily purchase suitable food in local pet stores which are prepared especially for the fry. If that is not available, you can also use high-quality flake food that is ground into a powder, as well as baby brine shrimp.

The normal flake food is too large for the fry; so try grounding it into a powder by using a coffee grinder or a mortar and pestle. This will be easier for the fry to eat.

Feed the fry several times a day and always give them a pinch of food. Remove any leftover food from the tank in order to keep the tank clean. Use a net to collect the leftover food.

Remember to change the water of the fish tank frequently in order to ensure that the fry is healthy. Use water from your normal aquarium in order to get the fry used to the environment that will eventually be their home.

Change about twenty to thirty percent of the water every day. This means that if your tank has about ten gallons of water, then change two or three gallons of water daily.

Carefully observe the progress of your fry. In about two months, the fry will be large enough to move to the standard aquarium. At that point, the fry will be as big as the mouth of the adult mollyfish.

Only move the fry to the bigger tank once you are sure that they can survive there. A premature movement may cause unnecessary tension between the fry and the other fish in the aquarium.

Transferring the Fry

First, you should make use of your breeding trap and then transfer the fry a few at a time to your normal tank. Use a standard aquarium net to transfer the fry if the two tanks are close to one another. If they are far from each other, then move the fry to a large bowl filled with water and carry them to your normal tank.

Try not to crowd the breeding trap. There should be enough room for the fry to move around freely. Transfer the fry a few at a time so that you do not overcrowd the trap.

Allow the fish to move around in the breeding trap before you release them into the larger tank. When you want to move the fry into the larger tank, just submerge the breeding trap into the water of the large tank and open the door. This will allow the fish to swim out into your normal tank.

Keep an eye on the newly introduced fry and make sure that the other fish are not harming them or are a threat to their existence.

Continue to do this until all your fry has been moved into the large tank. If any of the fry seems to be under stress, then move it back into the nursery tank and allow it to adapt before moving it again into the larger tank.

Breeding Mollies

Mollies are fairly easy to breed; so anyone can easily set up the tank and breed mollies. The first thing that you should do is create a beneficial breeding environment for the mollies.

The breeding scenario is really affected by the male-to-female ratio of your fish tank. Mollies are actually hierarchical fish, so the male with the biggest fins and the brightest colors is in charge.

For successful breeding, it is important to keep one male with multiple females. When the male goes under the female, they begin to copulate. If the whole mating process is successful, you will have baby mollies in about 60 days.

Once you are sure that your molly is pregnant, transfer her into a separate tank. Male mollies chase the female in order to copulate more, and this puts unnecessary stress on the female mollies.  Be sure not to wait very close to the birth date; remove the female molly from her aquarium as soon as possible.

Once the fry is born, you should place the mother molly back into the main aquarium, as there is a chance that the molly might eat its own babies.

Caring for Mollies

What to Feed Mollies

Mollies are actually omnivorous fish, so they can eat all kinds of food, including live, artificial, and frozen food. A thing that should be kept in mind is that mollies need a diet that is high in fiber; so vegetables and algae should be dominant components of their daily meals.

Wild mollies are known to eat lots of algae, and you can even observe this in your aquarium as it is quite common for the mollyfish to eat scraps of algae present on the decorations and glass of the tank.

You can give your molly fish flakes, boiled pieces of lettuce leaves, squash, and cucumbers in order to meet its vegetable requirements.

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Live food such as brine shrimp, tubifex, and bloodworm are also good additions to their meal plan. Feeding mollies is not the most difficult thing out there, but you really need to ensure that the vegetables are a large portion of their diet.

Always feed your molly with high-quality food, as poor-quality food weakens their immune system and makes them more susceptible to fatal diseases.


Mollies are known to be moderately aggressive, very active, and rather peaceful creatures. The behavior of the mollyfish changes if it is kept in a small overcrowded tank. They become more aggressive, and the small space puts stress on their health. The more room a molly has to roam around, the happier and healthier it is.

The best way to keep mollies is in a group, as they are very social. And remember to keep one male with at least two females. If the number of males surpasses the number of females, the environment of the tank will be anything but healthy.

The constant haunting by the males stresses out the female mollies. Males also do not get along with each other; so it is best to have a very spacious tank.

The mollyfish gets on very well with other tank mates, and it is better to keep them with mates of the same size. Mollies are known to stay civil with other fish.

Best Tank Conditions for Mollies

Temperature77-80 degrees Fahrenheit
Hardness20-30 dGH
Tank size20 gallons

Proper tank conditions allow your mollies to:

  • Live longer
  • Live healthier
  • Interact better in their communities
  • Combat against diseases
  • Remain stress-free

For a small group of molly fish, the ideal tank should be able to hold at least 50 liters of water, but as they are very active fish, a 100-liter tank should be bought to be on the safe side. Mollies grow to be up to 10 cm long; so it helps to have a large tank, as otherwise, it will be difficult for them to move around.

Mollies are more comfortable in water that is a little warm. The temperature of your tank should be around 25 to 27 degrees Celsius (77-80 degrees Fahrenheit). The fish also do not like drastic changes in the temperature of the tank. When you buy a heater, keep in mind that you need 5 watts per gallon of water in your fish tank.

The pH of the tank should be around 7 to 8 pH, while the hardness should be kept between 20 to 30 dGH. The mollyfish cannot live in brackish water, so it is best to put some salt into the water of your fish tank.

Water changes are also an important part of keeping healthy mollies. You should do a 20 percent water change every week in order to ensure the failure of ammonia and nitrates build up in the tank water.

Aeration and filtration are also vital. Make sure that you have a decent filter. Mollies are actually very messy, and they are constantly moving around and eating.

Having healthy bacteria in your fish aquarium is a must for your fish to survive. You can add bacteria from an already operating tank to your new tank in order to jump-start the process.

If you do not have one, then find a friend who has a fish tank, or you can even get one at your local pet store. The pet store will provide you with a chunk of its used filter pad to place in your new filter.

Add plenty of plants to your fish tank, as mollies feed on algae scrapings from the tank plants. Mollies spend most of their time in the middle and upper layers of the water. You should also provide the fish tank with ample lighting, stones, and snags, etc.

Mollies really love decorations. Mollies need places to hide from other bully fish. The timid fish gets pushed around a lot by other fish in the tank.

So there have to be ample hiding places in the tank for the molly to hide and feel secure. The more decorations and plants you have in your aquarium, the safer the molly will feel.

Types of Mollies

There are many different varieties of mollies, and the most common type of molly species held in aquariums is known as the short-finned molly. You can easily categorize mollies into two separate groups.

The majority of the mollies kept in aquariums are short-finned as they are easier to care for. The Sailfin mollies are a type that contains a fin comparable to the “sail” in ships. They require strictly regulated water temperatures and way more water volume.

Here are some kinds of mollies

  • Marble Lyretail Molly
  • Gold Dust Molly
  • Dalmatian Molly
  • Black Sailfin Molly
  • Balloon Molly
  • Black Molly
  • Harlequin Sailfin Molly
  • Platinum Lyretail Molly
  • Gold Doubloon Molly

Frequently Asked Questions

How many pellets should I feed my molly? 

It actually all depends on the size of the pellet. The stomach of the fish is approximately the same size as its eyeball. Your aim should be to provide enough that fill its stomach.

What is the life expectancy of the molly fish? 

Most molly fish generally live up to 5 years, but it depends on the variety of molly.

What other fish can mollies peacefully live with? 

Mollies live well with glowfish, guppies, tetras, and possibly gouramis.

Does the tank size affect the growth of the molly fry? 

The tank has no effect on the growth of the fry unless it is too small or overcrowded. A medium-sized tank is preferred; as in it, they can move around comfortably. In a tank that is too big, the fry have difficulty locating their food.

How can I grow my fry faster? 

There is, in reality, no way to speed up the rate with which your molly fry grows. But in order to ensure their health, you can provide them with a safe and secure environment with ample food and hygienic conditions.

Do I need an air pump? 

If you have a running filter in your fish tank, then you do not necessarily need an air pump, although it does provide a good backup option for when your filter fails. The sponge filter does the same thing and also filters your water. The sponge filter will be able to save your tank all by itself if your filter fails.

Should I use a bubbler or an airstone? 

The thing you need to worry about is that there should never be insufficient oxygen in the tank, so too much oxygen is fine. Mollies do not actually mind the air bubbles, so a bubbler is a safer option.


In conclusion, it’s important to be prepared and knowledgeable when you have a pregnant molly with babies in your aquarium. Creating the right environment, observing their behavior, and caring for the fry are key to their well-being. With the right approach, you can enjoy the unique experience of raising molly fry in your tank.

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Nadine Oraby

My name is Nadine; I am a passionate writer and a pet lover. People usually call me by the nickname “Joy” because they think that I am a positive and joyful person who is a child at heart. My love for animals triggered me to create this blog. Articles are written by vets, pet experts, and me. Thanks for visiting. Your friend, Nadine!

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