How To Tell if My Molly Fish is Pregnant?

Mollies can be crazy when it comes to reproducing. For a rough understanding, a single molly can give birth to 120 babies at a time!

But what’s even grimmer is that most of these babies get eaten by the adult mollies themselves!

To prevent either of the two outcomes, recognizing if your molly is pregnant or not is crucial.

How do you know if your molly is pregnant? A pregnant molly will develop a swollen belly with a dark spot or line in the center of their abdomen. They will also become slightly aggressive and eat more during pregnancy. Near the laboring stage, a pregnant molly will go into hiding and stop eating for the most part. 

Even after you find out if your molly is pregnant or not, you still need to know how to protect the babies.

To find out, keep reading ahead:

Signs That Your Molly Is Pregnant

During pregnancy, a molly goes through several physical and behavioral changes that can be easily identified by a keen eye. The first signs become visible 7 to 10 days after fertilization, while others appear throughout the pregnancy. 

It’s important to keep a close eye on your molly throughout the pregnancy period, specifically during the last few days to prepare for the laboring stage. With that in mind, here are some of the most common ways to identify if your molly is pregnant: 

1. Swollen belly with a dark spot

The most apparent and easiest sign to spot in pregnant molly is a swollen belly. You will also notice a blackish spot or line running down her stomach, which are the eyes of the fry. The pregnant molly’s body will also continue to become plumper and rounder as her pregnancy progresses.

However, this sign is usually relevant in the last few weeks of pregnancy as mollies don’t develop a swollen belly immediately after fertilization. Moreover, the black spot isn’t visible on darker colored mollies, so you will have to keep an eye out on their abdomen. 

2. Aggressive and isolated behavior

It’s quite normal for mollies to become protective and slightly aggressive towards other tank mates during pregnancy. This is an instinctual defense mechanism, but the aggression is barely dangerous or harmful. But more than fighting, mollies prefer hiding and isolating to protect themselves and their soon-to-be-born fry.

In the last week of gestation, you’ll notice that your molly will become significantly more isolated and will spend most of its time near the bottom of the tank. What they’re actually doing is finding a safe place to give birth where they can be safe from attacks and protect their fry as well. 

3. Changing appetite

After fertilization, a molly’s appetite starts increasing to meet her increasing nutritional needs. You will notice that she become extra active during feeding time and might even fight other fish for food, so make sure there’s enough to eat for everyone. 

See also  Pregnant Molly with Babies – What You Should Know?

But as the laboring stage nears, the molly’s appetite will start decreasing, and she will spend more time in isolation. Though it might be difficult to identify when a molly is eating more or less, you will notice a change in their eagerness to eat if you keep a close eye on them.

How To Know Your Molly Is About To Give Birth

Mollies normally gestate for about 20 to 40 days from becoming fertilized to giving birth. Near the end of the pregnancy period, a molly will exhibit signs that they’re about to give birth. Those signs include:

  • Completely isolating in caves and plants
  • Not showing interest in eating or coming near the surface
  • Swimming extremely slowly or staying stationary
  • Swollen belly develops a V-shaped bulge

When you identify these signs, there’s a good chance that your molly is very close to giving birth. This is usually a good time to start making preparations for the laboring process. 

How To Save Molly Fry

Mollies have a pretty bad reputation when it comes to parenting. Once the fry are born, most or all of them are eaten by the adult mollies, including the mother! To save the fry from this torturous death, it’s important to make preparations before your molly gives birth. 

To do this, you will need to arrange some equipment and follow basic instructions so that the fry can get to live and grow up without being eaten.

1. Separate the pregnant molly

The best way to protect fry from being eaten is to separate them from the adult fish before they’re born. You can do this in two ways; by moving your pregnant molly to a separate tank or a breeding box. 

Shifting the pregnant molly to a new tank is typically the best option as it gives the fry more freedom and allows you to give them special attention. You can adjust the temperature and water parameters as per their needs, and the fry will also have more space to swim safely in a separate tank.

However, you need to prepare this tank in advance. To do this, make sure that the water parameters are the same as your main tank so that your pregnant molly doesn’t become stressed after being shifted.

On the contrary, if you plan to use a breeding box, you don’t need much planning. Just make sure that the aquarium’s water is in its best condition with zero ammonia and nitrites, and the tank has enough hiding space.

2. Restrict the tank or breeding box for fry

Once your pregnant molly is done giving birth, she will start cannibalizing her fry just a few hours after birth. Because of this, you need to take out the mother from the breeding box or tank as soon as she’s through with labor.

See also  How Long Can Fish Go Without Oxygen? Survive A Power Outage!

Mollies give birth to anywhere between 20 to 100 fry in a single pregnancy. Because these fish are livebearers, they give birth to live young instead of eggs. One way to identify if the molly’s laboring stage is over is to notice her swimming pattern. 

If she’s swimming more freely and quickly than before, she probably won’t birth any more fry. This is the right time to remove her from the tank or breeding box and place her back into the main tank.

3. Add plants and hideouts in your tank

Having lots of dense plants is crucial for the young fry’s survivability, whether they’re living in a separate tank, breeding box, or the main aquarium. Usually, this should be done before the pregnant molly gives birth to the fry so that they have a place to hide.

Freshwater fish fry usually take shelter in floating plants right after birth. So try to have at least two to three types of floating plants in your tank or breeding box. You should also have dense plantations at the bottom of the tank so the fry can take shelter as they grow up. Some great plants for mollies include duckweed, frogbit, hornworts and java moss.


What is the best water temperature for mollies?

The ideal water temperature for mollies is 72 – 78°F or 22 – 25°C. Molly fry also require the same temperature but can have faster digestion and growth in water that’s two to three degrees warmer than the ideal range.

Do mollies die after giving birth?

Some mollies die after birth due to immense stress from labor as they can give birth to up to 100 fry at a time. They might also succumb due to previous diseases and defects or extreme water conditions in the aquarium.

At what age do molly fish breed?

Male mollies become sexually mature at 12 months of age, while female mollies can reproduce after turning six months old. After that age, these fish can breed and give birth to fry.

How frequently do mollies breed?

Mollies can breed right after giving birth, which takes about 20 to 40 days on average, and will continue to reproduce for 2 – 2.5 years after becoming sexually mature. Moreover, female mollies can store sperm after mating, so they can get pregnant several times after breeding without needing a male molly.

What should you feed molly fry?

Molly fry should be fed the same diet as adult mollies, just in smaller pieces. Some great foods for molly fry include brine shrimp, flake food, bloodworms, daphnia, all chopped up into very tiny pieces.

Photo of author

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!

Leave a Comment