Why Do Mollies Die After Giving Birth? (Reasons & Solutions)

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The longer I grew mollies in my fish tank, the more frequently I saw how the female ones kept dying after spawning. At first, I took it as a natural occurrence, since offspring delivery is a stressful process. But I saw that in some cases, the females are perfectly capable of surviving after delivery. That was when I began to research the topic a little deeper.

Mollies typically die after giving birth due to severe labor strains, secondary to long delivery duration, hostile environment, and inappropriate water conditions. Female mollies also die after delivery due to genetic defects and underlying diseases, such as flukes, fin rot, and ammonia burns.

As we move forward, I will share a few useful techniques to prevent pregnant molly fish from dying after delivery. Those tricks had worked for me before, and I highly suggest that you implement them in your tank.

Also Read: Pregnant Molly Fish 101

What Causes Mollies To Die After Giving Birth?

Mollies are livebearers.[1] Females reach sexual maturity after six months. On average, they give birth every 28 days, and they can produce as many as a hundred fry at a time. However, sometimes female mollies die after giving birth. 

This occurrence is not usual. Fish are not supposed to die after spawning. Yet, it happens all the time. The phenomenon rarely concerns professionals because they are accustomed to it. They also know what to do to prevent the issue from reoccurring down the line. 

Those who are relatively new to fishkeeping are not as knowledgeable, which is why they tend to panic. The right approach is to understand why this issue is happening. Generally, the death of mollies after giving birth can be credited to a variety of factors:

1. Labor Difficulties

Pregnant mollies do not necessarily encounter the same experiences as humans. Their bodies are very different. For instance, there is no placental connection between the fertilized eggs and their parents. Additionally, female mollies do not parent their young ones. In fact, they are more than likely to eat them.

However, mollies and humans share one thing. Giving birth is a stressful and strenuous experience for both species. You see this in other livebearers as well. Some of them will experience dramatic weight loss after giving birth.

Human beings die all the time as a result of the stress of labor. This happens in mollies as well. It isn’t the most prominent cause. Most mollies are strong enough to survive despite the rigors of the birthing process. But a few succumb to the strain.

2. High Delivery Frequencies

Any strain mollies experience during labor is further compounded by frequent births. While mollies are more than capable of giving birth every 28 days, it is in their best interest to give them breaks in between. Some aquarists believe that frequent births can shorten a fish’s lifespan. 

Whether or not that is true, mollies that give birth every 28 days without a break are more likely to succumb to labor strain. That strain will eventually kill them. You have no way of identifying the pregnancy that will lead to death until it happens.

3. Birth Duration

This is another element that mollies share with humans. The duration of the birthing process tends to vary. Some mollies give birth quickly. Others take much longer. The process is supposed to take anywhere between one hour and 24 hours. Naturally, the longer the birthing process, the more strain the molly fish is forced to endure. 

Some fish can handle that strain. Yet, others cannot. While giving birth, female mollies find it challenging to catch food and protect themselves. Such stressful conditions may end with death, especially if the female was already sick or shares a tank with aggressive tank mates.

4. Breeding Tanks

As was noted above, mollies are not the best parents. They will happily eat their young ones. And even if they don’t, community tanks are dangerous places for young fish. One way of protecting the fry is to place them in a separate tank just before giving birth.

This allows them to give birth in peace, free from the conflicts that can sometimes emerge in community tanks. You can move the adult fish back to the main tank once the birthing process ends. That allows the fry to grow up in an environment free from danger.

This is a rational and effective means of protecting your pregnant molly and its young ones. However, the process of moving a fish from one aquarium to another is pretty stressful.[2] In some cases, the experience is so traumatic that the fish dies after giving birth.

It is worth mentioning again that stress is bad for fish. It ruins their health. And unfortunately, the simple act of moving your molly fish to a breeding tank may do more harm than the aggressive fish from which you want to protect it.

5. Male Aggression

Because female mollies are often exhausted from the stress and strain of giving birth, they are not in any condition to contend with aggressive behavior. Unfortunately, where mollies are concerned, the males are a far more significant threat than any massive, more volatile fish you might have in the tank.

Male mollies tend to harass their female counterparts. That is why beginners are encouraged to keep three females for every male molly in the tank. That is the only way to alleviate the stress that male mollies can induce when they pursue the female mollies.

It is more than possible for a male molly to badger and harass a sick and exhausted female molly to death, especially when it has just given birth. If you are accustomed to the way the males treat the females in your tank, you will probably ignore this behavior when the females give birth because you do not realize that, in such a state, they lack the strength to withstand this harassment.

6. Genetics & Diseases

Some fish are just weaker than others. They have anomalies and defects that encourage complications to arise during pregnancy. These complications, such as fry becoming stuck in the birth canal, can lead to death in the aftermath of the birthing process. You cannot do anything to resolve genetic defects. 

A pre-existing illness will also make it difficult, if not impossible, for a female molly to withstand the strain of giving birth. After all, diseases like fin rot and the flukes eventually weaken the fish, compelling them to lie listlessly at the bottom or to hover in place.[3] That is because the sick fish cannot muster the strength to move. A molly fish in such a state cannot be expected to live and thrive after giving birth.

7. Inadequate Water Parameters

Everything goes back to the stress and the strain of the birthing process. Your fish must be healthy and robust to give birth without complications. However, that won’t happen if the parameters in the tank are wrong.

Mollies need temperatures ranging between 72 and 78 degrees F, a pH ranging between 6.7 and 8.5, and the right hardness.[4] You must also keep toxins like ammonia, nitrates, and nitrites under control, not to mention maintaining proper hygiene.

A poorly maintained tank is going to weaken your molly fish, making it sick. A sick fish is unlikely to survive long after giving birth, mainly if its breathing is labored because its gills were burned by ammonia. Naturally, female mollies that aren’t able to breathe correctly beforehand are less likely to survive after delivery.

Also Read: Why Is My Molly Not Giving Birth?

How To Keep Mollies From Dying After Giving Birth?

While the death of mollies after giving birth is relatively common, there are steps that you can take to reduce the chances of this phenomenon occurring, for instance:

1. Facilitate The Labor Process

It isn’t always possible to make the birthing process stress free. But you can make it smoother and less complicated by making the fish comfortable. Give the molly a place to hide where it can give birth without worrying about aggressors.

One option is to add plenty of plants so that the fish has numerous hiding places to choose from. Even with the risks involved, you should also consider using a breeding tank, especially if the fish lives in a community tank. 

A separate tank will give your pregnant molly peace of mind, eliminating the threat of bullies. When it comes to breeding tanks, I highly recommend the Capetsma Fish Breeding Box (link to Amazon). That is the precise model that I use, which was able to keep my pregnant mollies and the fry, perfectly safe.

I also recommend facilitating the process by removing all sorts of distractions. Try placing the tank in a location with no human traffic. You should also stay away during spawning as much as possible. Your presence could delay the birthing process.

2. Ensure Proper Water Conditions

Try maintaining a pristine tank. Change the water regularly to eliminate toxins. Also, check the filter and the heater to ensure that they are operating optimally. Lastly, test your water frequently to make sure that all the parameters are within reason.

When it comes to testing kits, I highly recommend checking the API Aquarium Test Kit (link to Amazon). That will help you monitor toxins such as ammonia, nitrites, and nitrates regularly, preventing unexpected death and diseases. Keep in mind that this particular kit is designed for freshwater aquariums so that it won’t work on saltwater ones.

Even before your mollies mate, you need to ensure that they are housed within a sizable tank of at least 10 gallons. Additionally, avoid overcrowding. Small, overcrowded tanks will induce the sort of stress that leads to death during or after giving birth.

Your molly needs a healthy, peaceful environment that is conducive for the pregnancy and the birthing process. A molly fish living in a well-maintained tank is less likely to fall ill.

3. Mitigate Male Aggression

If you don’t want to move your molly fish to a separate tank to protect it from the attention of its male counterparts, add a few more females to the aquarium. This will divert the attention of the male mollies.

You should also add more plants and decorations to give the female fish more hiding places. If the aggression of the male fish has refused to abate, add a divider to the tank. This will keep the male mollies away from the female fish. For your convenience, I attached a YouTube video above that describes just that.

4. Treat And Prevent Disease

Keep a close eye on your pregnant molly fish. You need to catch any signs of illness as early as possible.[5] Try to treat the diseases before the mollies give birth. The approach you will take is related to the illness in question.

Some diseases are treated by raising the temperature. Others are eliminated by adding aquarium salt. You can also utilize one of many antibiotics and drugs on the market. In many cases, a water change will make all the difference.

Many illnesses and infections can be traced back to a dirty, poorly maintained tank. Improving the tank’s conditions will debilitate the strength of various diseases while also empowering the molly’s immune system to fight back. That is why you should keep the tank as clean as possible. Remove uneaten food and rotting organic matter such as dead plants and fish.

Don’t forget to give your mollies a balanced diet.[6] They are omnivores, which means that they eat both plants and animals. You shouldn’t underfeed or overfeed them. A balanced diet typically consists of bloodworms, brine shrimp, lettuce, and zucchini, not to mention flakes and pellets. That will keep your molly fish healthy enough to fight off diseases and remain stable in the face of the strain of the birthing process.

Also Read: Do Mollies Eat Their Babies?


Stress is the most common cause of death in pregnant molly fish. When the strain is too severe, female mollies are not likely to survive after spawning. That could be when the birth is prolonged or too frequent, for example. The tank mates and water conditions also play a central role in this phenomenon. 

To keep female mollies from dying after delivery, keep the environment as ideal as possible. For a start, use a breeding tank, while moving the pregnant molly as gently as you can. That will keep hostile fish such as male mollies away.


  1. https://www.aquariumnexus.com/pregnant-molly-fish/
  2. https://www.myaquariumclub.com/pregnancy-in-female-livebearing-fish-1923.html
  3. https://www.aquariumnexus.com/molly-fish-diseases-parasites-remedies/
  4. https://www.fishkeepingworld.com/molly-fish/
  5. https://guppyexpert.com/guppy-fish-died-after-giving-birth/
  6. https://www.aquariumnexus.com/mollies-keep-dying/