Do Mollies Have All Their Babies At Once?

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I got pretty excited as I saw the fry coming out of my pregnant molly fish. However, a day later, the molly fish was still bloated. That got me wondering; do molly fish have all their baby at once or do they deliver the newborns in batches?

Mollies have their babies in a certain period, which can last a few days. During that time, baby mollies will exit the birthing canal one by one. Eventually, the female molly will deliver between 40 and 100 fry. The birthing period is not likely to proceed for more than a couple of days.

As we move forward, I will show you in which cases the birth of baby molly fish may get complicated, including potential abortion. I’ll also offer a valuable way to prevent this from happening. That will mainly focus on adjusting the water conditions for pregnant mollies.

Also Read: Pregnant Molly Fish 101

Do Mollies Have All Their Babies At Once?

Mollies are easy to breed. If you have both genders in a tank, they will multiply at a relatively rapid pace.[1] But because they can produce as many as a hundred babies in one go, people cannot help but wonder whether the creatures push all those babies out at once.

The birthing process among mollies has several essential dimensions. They include:

1. The Number Of Fry

Many resources say that mollies give birth to all their babies at once. But that doesn’t mean what a lot of people think it means. Mollies give birth to live fish. The male fish will fertilize the eggs inside a female molly’s body.

Those eggs will hatch inside the female fish and will develop for 50 to 70 days until the female molly is ready to push them out. 

However, if the female molly has one hundred babies in its womb, they cannot exit the birthing canal simultaneously. That isn’t possible. The molly fish wouldn’t survive the birthing process.

When people say that mollies give birth at once, they mean that the creatures will push all their fry out within a single period. That period could last minutes or hours. 

Either way, many aquarists expect their mollies to evacuate all the babies at once. They don’t expect to see more babies escaping the molly’s anal vent several days later. Not everyone agrees with that assessment. 

Some aquarists are convinced that mollies can choose to space out the birthing process. For instance, they may push out 40 babies today and 20 babies a week later. The mother can even hold onto the second batch of babies, refusing to give birth to them.

Regardless of whether your mollies give birth at once or over several days and weeks, the fry will leave the womb one at a time. The fish may push them out in quick succession or in batches, pausing for several hours in between.

Guppies, the molly fish’s close cousin, have similar patterns. They can introduce pauses in between batches that can last days.[2] The trend you will see depends on the fish and the conditions in the tank. Don’t expect every molly fish to manifest the same birthing behavior.

2. The Birth Duration

Labor among livebearers like mollies and guppies can last anywhere between two and six hours.[3] Though, on occasion, the birthing process can exceed 12 hours. It can even last days if unexpected complications have prevented the babies from escaping the fish’s womb.

Six hours is a healthy average. Labor that lasts 12 or more hours should concern you. Though, it doesn’t necessarily mean that something is wrong. If your fish isn’t in distress, let it give birth at the pace it has chosen.

3. The End Of Birth

You cannot keep female mollies and their babies in the same tank. Put the pregnant molly in a breeding tank, wait for it to give birth, and then move it back to the community tank. It is essential to separate the female from the fry, so the fish doesn’t eat its babies.

However, you should wait for the mother to push all the fry out before moving her to the main tank. But that raises a question. How can you determine that a molly fish has finished giving birth? Unfortunately, this question doesn’t have an answer. 

You can use the duration of past pregnancies to estimate the duration of current pregnancies. For instance, if the previous fish took six hours to give birth, you can assume that your pregnant molly has finished giving birth after six hours.

But you can’t trust this method because, as was noted above, some mollies can give birth over the course of several days. Some mollies look empty once they eject all the fry. If that doesn’t happen with your mollies, give it 12 to 24 hours. 

If the fry have stopped coming, you can move the mother back to the main tank. Make sure the main tank has plenty of hiding places. That way, if the fish produces more fry, they can still survive in an aquarium with adult fish that want to eat them. 

Ultimately, you have to make an educated guess. Fortunately, mollies breed quickly and easily. Even if you lose some fry because you sent the female back to a tank with predators while it still had fry in the womb, the female will make more babies in a few weeks.

Also Read: When To Separate Pregnant Molly Fish?

Can Mollies Fail To Give Birth?

Molly fish that release fry sporadically over several hours and days are not a problem if the fish is not in distress. If you place the fish in a peaceful environment, it will eventually push out all the fry.

A more significant concern is mollies that are swollen with babies, and yet, after several hours, they have only produced a small number of fry or no fry at all. 

Fry can get stuck inside a pregnant molly. Sometimes, you can see the stuck fry because half of it is still inside the mother while the other half is sticking out of the vent. In other cases, you can’t see the obstruction. But you can tell that the molly is unhappy because it has failed to give birth. 

Some people solve this problem by massaging the area from the front of the stomach to the vent. You do this gently with your forefinger. If the pressure applied is firm, you will unplug the vent.

If you have the experience, you can use tweezers to pull the fry out of the way. The fry won’t survive. The chances of the mother surviving are also low. Don’t be surprised if she bleeds internally.

Abortions are another concern. They can extend the birthing process because the fish is trying to expel both the healthy fry and their unhealthy underdeveloped counterparts.

Aborted fry are still attached to their yolk sac. Don’t expect them to survive. Mollies can also expel nonviable eggs during this period.

Also Read: Why Is My Molly Not Giving Birth?

Will Bad Water Conditions Interfere With Molly Fish Birth?

Poor water conditions can extend a fish’s labor past the typical duration. Extreme temperatures, high nitrate levels, and the wrong pH cause stress. A stressed mother can easily take days to give birth. It may also abort the fry.[4]

This is why many aquarists prefer to keep pregnant mollies in a separate tank. They want the creature to give birth in a peaceful environment, away from male mollies and other fish with violent streaks.

These are the ideal water conditions for pregnant molly fish: 

  • Temperature: 77-80 degrees F (25-27 degrees C) 
  • pH: 6.7-8.5 
  • Hardness: 20-30 KH 
  • Ammonia & Nitrites: 0 ppm 
  • Nitrates: <20 ppm

To measure the ammonia, nitrates, nitrites, and pH, I personally use the API Water Test Kit (link to Amazon). There are many bundles out there, although this one lasts for eight hundred measures, making it highly cost-effective.

If you notice that the toxins are too high or the water is too acidic, try not to make drastic changes. Typically, I would suggest performing frequent water changes. However, these may stress pregnant mollies even more.

Instead, I suggest considering water conditioners, such as Seachem Prime (link to Amazon). Adding a few drops of this will buffer your water and neutralize toxins like ammonia and nitrates. And even if the conditions are okay, a water conditioner will prevent things from deteriorating in the future.


Molly fish have all their babies at once, although the birthing period may differ from one fish to the next. If your molly fish fails to give birth after twelve hours, she may have aborted her fry, or her eggs may not be viable. 

The fry will exit the canal one by one within the delivery window. They will not pop out all at the same time. To ensure that this process goes smoothly, I suggest adjusting the water conditions for pregnant mollies. Focus on the temperature and pH. 

I also suggest checking for toxins, including ammonia, nitrates, and nitrites. If you noticed anything unusual, consider a water conditioner. Using a few drops of these products will cause less stress than drastic water changes.