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Why Is My Molly Not Giving Birth? (With Solutions)

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Mollies are pretty convenient to grow, although not that easy to breed. More than once, my female molly fish had failed to give birth, even though I did everything to encourage the process. To solve the issue, I began researching all the possible reasons why molly fish refuse to give birth.

Factors that will prevent your molly fish from giving birth are mostly environmental and include aggressive tankmates, inappropriate water conditions, and sudden aquarium changes. Also, using a breeding net could stress your molly and inhibit it from bearing of offsprings.

As we move forward, I will elaborate on the steps you should take to ensure that your pregnant molly fish eventually give birth. Then, I will explain what to do once this happens, so that your fry remain healthy and alive.

Also Read: Pregnant Molly Fish 101

Why Is My Molly Not Giving Birth?

Mollies are livebearers.[1] In other words, they give birth to live fish. They are curious creatures because their breeding habits are somewhat tricky to track. However, female mollies must mate with male mollies to give birth.

They need a male’s sperm to fertilize the eggs in their bodies. But female mollies have been known to give birth in tanks that have no males. This feat is made possible by a molly fish’s ability to store sperm, using it to fertilize its eggs several months down the line. 

But that isn’t the molly fish’s only quirk. Mollies don’t always give birth on schedule. This can become a source of frustration for aquarists that have been known to spend weeks waiting in vain for a pregnant molly fish to give birth. 

Believe it or not, such occurrences are quite common, and they have been blamed on factors such as the following:

1. Genetics

While it is relatively common for pregnant mollies to hold off on giving birth, no one would blame you for worrying. After all, plenty of aquarists whose mollies delayed in giving birth will tell you that their fish eventually produced dead fry. You should definitely approach this issue with concern.

That being said, these delays in giving birth are not always caused by negative stimuli in the tank. Sometimes, the fish’s genetics are at fault. In such cases, you are encouraged to apply some patience.

Some aquarists have testified that delays in giving birth ended terribly for their mollies. Yet, others will tell you that their mollies eventually gave birth to healthy fry and did not suffer any health consequences due to the delays.

If you are new to mollies and your tank is pristine, you should consider the possibility that the delays your molly fish is exhibiting are typical. Wait and see what happens. If the delays end in disaster, you can start looking for an alternative explanation.

2. Breeder Nets

It is relatively commonplace for aquarists to keep pregnant mollies in a breeder net. This can encourage a reluctant pregnant molly fish to give birth, especially if it was initially hesitant to release its fry in a tank populated by fish that might present a threat to its fry.

However, some mollies do not like breeder nets. In fact, they do not like being moved at all when they are pregnant. Moving them can induce the sort of stress that will either discourage them from giving birth or encourage them to abort their babies altogether.

It depends on the personalities of the individual fish. Some species are comfortable in breeder nets and will freely give birth in those. However, others may feel intimidated. You have to experiment to determine the preferences of your mollies. 

3. Bullying Tankmates

As mentioned above, mollies can refuse to give birth in tanks populated with threats such as fellow mollies and other aggressive fish. If your molly fish is a victim of bullying, it has even more incentive to resist the urge to give birth.

Some people resolve this issue by using a breeder net. However, your pregnant molly could still feel threatened if she can see the aggressors swimming by. Still, if your mollies don’t want to be moved, you can add a divider to the tank.

Also Read: Why Do Mollies Die After Giving Birth?

4. Abrupt Changes

Drastic changes in the aquarium can cause delays. If you keep rearranging the objects in the tank, you may generate uncertainty in your mollies. The same thing can happen if you change the lighting or if the mollies were only recently added to the tank.

In such situations, patience is the only solution. You can also add plants and decorations to make your mollies feel as in their natural habitat. The presence of proper hiding spots will allow your mollies to alleviate their stress, overcoming their sense of fear and uncertainty.

5. Inappropriate Water Conditions

Poor conditions in the tank will encourage delays in delivery. Mollies need a temperature ranging from 77 to 80 degrees F, a pH ranging from 7 to 8, hardness ranging from 20 to 30 dGH, and a tank of at least 20 gallons. 

The appropriate conditions will produce healthy, happy, social, stress-free mollies that will give birth on time. The wrong parameters, overcrowding, and the presence of toxins like ammonia will cause the sort of stress that will complicate your molly fish’s pregnancy.

To support your molly’s pregnancy, you must maintain a pristine, planted tank and a stress-free environment. As was mentioned, you should keep specific parameters such as pH and ammonia in the desired range. You can easily do so by using testing kits like the API FRESHWATER MASTER TEST (link to Amazon).

How Can You Tell If Your Molly Is Pregnant?

Before you start complaining that your molly fish has refused to give birth, first confirm that it is actually pregnant. Some cases could be misleading, like a sick molly female that got swollen due to an ailment. Therefore, you should look for additionals signals.

Typical signs for a pregnant molly fish include:

  1. Swollen Belly – The belly of a pregnant molly will gradually swell as the offsprings grow.
  2. Dark Spots – Your pregnant molly fish will develop a triangular spot near the anal vent.
  3. Swimming Behavior – Pregnant mollies tend to move slower. They also eat more food and avoid other fish in the tank. 
  4. Caution – Pregnant molly fish spend their time in a safe, isolated corner. They may be found behind the filter or at the bottom corners of the tank.
  5. Fry Development – If you make close observations, you will see the fry’s eyes in the fish’s belly.

How Long Does It Take For A Molly To Give Birth?

Molly fish have a gestation period ranging between 50 and 70 days, depending on the type of molly fish. They can become pregnant every thirty days by either mating with a male molly or fertilizing their eggs with the sperm they stored.

Female molly fish can produce anywhere between twenty to one hundred fry during each session.[2] It may take between 1 hour and 24 hours for the birthing process to complete. When this happens, you should prevent all possible distractions and keep a distance from the tank.

When Should I Separate My Pregnant Molly?

For many pregnant mollies, the transition to a separate tank is stressful. The female fish does not acknowledge your positive intentions. That is why you should do so gently, and precisely on the right gestational stage.

You should separate your pregnant molly once it is close to giving birth. These mollies will develop a v-shape at the bottom of their stomach. At this point, they will also become more reclusive and avoid encounters with other tankmates.

What Do You Do When A Molly Has Babies?

Once your molly fish gives birth, you cannot trust it to take care of the babies. It will probably eat them all.[3] As such, you have to take responsibility for them. This is what is expected of you:[4]

1. Use A Breeding Tank 

You should set up your tank before your fry are born. Once you realize that your molly fish is about to give birth, move it to the breeding tank. Otherwise, the other fish in the main tank will eat the fry. 

The presence of aggressive tankmates could also prevent your pregnant mollies from giving birth from the first place. Separating it will give the molly fish the conducive environment it needs to give birth successfully.

2. Maintain Ideal Tank Conditions

Aim for 5-20 gallons depending on the number of fry you plan to raise. The tank needs a filter, preferably one with a foam or mesh cover to protect the young mollies. Some filters are too dangerous and can suck up your fry. If you think your filter presents this danger, you can apply a nylon strip.

Also, add a reliable heater to keep the temperature in the right range (72-84 degrees F). Use a thermometer to monitor the temperature; it must remain consistent. Your tank also needs plants; טou can use either natural or artificial ones. Prioritize broad-leafed varieties.

3. Feed The Fry Properly 

Once the fry are born, you should feed them. Fortunately, they can survive on the same meals you feed adult mollies.[5] That includes flakes, pellets, frozen, and freeze-dried foods. However, you have to grind the food to a size that the baby mollies can consume.

Try maintaining a regular schedule and endeavor to remove all uneaten food before it rots and corrupts the tank. This can be achieved with a net. Keep in mind that accumulated leftovers could raise ammonia levels and compromise the fry’s health.

Keeping the tank clean is crucial. It isn’t enough to install a filter. It has a role to play, but there is a limit to what it can do. Try to make daily water changes of roughly 20 percent. This will prevent toxins like ammonia and nitrates from accumulating.

4. Relocation To The Community Tank

If everything goes according to plan, your fry will reach a stage in two months where you can move them to a standard tank. At this age, they are too large to fit in the mouth of an adult molly. As such, they are less likely to get eaten.

Use a breeding trap to help the fry acclimate to their new tank. Install it on the standard tank side and use it to introduce your fry a few at a time. Overcrowding is as problematic for breeding traps as it is for aquariums.

Make sure the fry in the trap have enough room to swim freely. Moving the young mollies this way might take longer than you would prefer, but it is the safer option. To do that, you may follow the Youtube video embed above.

Keep the fry in the trap for an hour or so before allowing them to enter the aquarium. However, don’t be so quick to abandon them at this stage. Watch them during these initial moments. Ensure that none of the other fish are attempting to harm them.

If you observe signs that suggest that any of the fry are not ready for the standard tank, move them back to the breeding tank. Give them a few more days before attempting to move them to the standard tank.

Also Read: Do Mollies Have All Their Babies At Once?


If your molly female does not give birth, it could be related to genetic factors. Some mollies merely need more time. However, that could also indicate an issue, such as stressful conditions or a bullying tankmate.

To encourage your pregnant molly to move forward, you should keep it in a relatively large aquarium, at least 20 gallons. You should also avoid overcrowding the tank. A separate breeding tank is probably your best choice.