When To Separate Pregnant Molly Fish?

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Realizing that your molly fish is pregnant can be exciting. However, it is also pretty complicated. For example, you must know when to separate the mother from the fry. Otherwise, she might eat them pretty quickly. Luckily, over the years, I gained some experience on this topic.

It is best to separate pregnant molly fish from her tankmates as soon as the fish shows signs of pregnancy. The ideal choice would be taking away the tankmates while leaving the pregnant molly in the original tank. Then, the mother should be separated from the fry after she’s done giving birth.

As we move forward, I will elaborate on the timing of separating a pregnant molly fish from her fry. Then, I’ll discuss the different ways you can do that, including making your own divider.

Also Read: Pregnant Molly Fish 101

When Should I Separate My Pregnant Molly?

It is common practice to separate a pregnant molly fish from its tankmates. The goal is to create a stress-free environment where the fish can give birth. But when is the right time to move the molly fish?

Well, it depends on who you ask. You will encounter three primary trains of thought where this question is concerned:

1. Once There Are Signs Of Pregnancy

Some people prefer to separate the female molly when they notice signs of pregnancy.[1] Those signs include aggression, a dark triangular spot near the anal vent, and a swollen belly.

It can take a molly fish as many as 70 days to give birth. Moving the fish to a separate tank will make those 70 days as painless and stress-free as possible. Pregnant mollies prefer to hide, responding aggressively to fish that invade their territory.

Some mollies won’t stop at simply defending their corner of the tank. They will lash out, attacking their tankmates wherever they can find them, especially if they don’t have enough hiding places. 

They can turn the tank into a miserable place for the next several weeks. Moving the fish to a separate tank protects the pregnant molly and its tankmates from unwanted aggression.[2]

2. Just Before Birth

Many aquarists encourage beginners to separate pregnant mollies shortly before they give birth. Some people wait until the fish is just moments away from releasing the fry before shifting the creature to a separate tank.

But that approach is risky. First of all, pregnancy induces significant amounts of stress. Moving the fish during the most stressful moment of its pregnancy could generate even more stress. In the best-case scenario, the molly will abort the babies. 

In the worst-case scenario, it will die during or after giving birth. Additionally, it takes a skilled and highly experienced aquarist to determine whether or not the molly is on the verge of giving birth. The layperson won’t even realize that the molly fish is in labor until it is too late.

If you must wait until the molly is about to give birth, give yourself as much room for error as possible. That means moving the fish one or two weeks before it gives birth. 

Look for all the obvious signs of imminent labor, including:

  • Activity – A molly fish near its due date will become less active. It may spend more time than usual sitting or hovering in one spot.
  • Hiding – Pregnant mollies near their due date will stay out of sight, frequenting hiding spots behind plants and decorations. 
  • Food – The creature’s appetite will disappear altogether. She may also become more aggressive during this period.

If you think you interpreted these signs accurately, you should separate the fish. It is better to move it too early rather than wait until it is too late. 

Yet, some people dislike this practice. Even if the molly is one or two weeks away from giving birth, they believe that moving it at such a late stage can still induce more stress than the fish can handle. 

That is why many aquarists encourage separating the molly fish several weeks before its due date (while the creature is strong and healthy) or keeping it in the community tank.

Also Read: How Can You Tell If A Molly Is About To Give Birth?

3. After Your Molly Gave Birth

The primary goal of separating a pregnant molly is to protect its fry. You don’t want the other fish in a community tank to eat the fry. And once the fry are born, you have to move the female molly to another container for a day or two before returning it to the community tank.

Keeping the mother and its babies together is a recipe for disaster because the mother will eventually eat the fry. People do the same thing for guppies, close cousins to molly fish.[3]

However, if your only objective is to protect the fry, you don’t have to move the mother. Wait for her to give birth and then transfer the fry to a new tank. Scoop them out of the water with a cup. Don’t use a net.[4]

This practice is challenging because the adult fish may get to the fry before you can move them. Also, what if you miss one or two baby fish? You may strand them in a community tank filled with large fish that will most likely eat them.

That is why I also suggest considering a fry trap. You can easily do that with a plastic bottle. Here is an excellent Youtube video that will show you how it’s done:

How Do I Separate Pregnant Molly Fish?

It is worth noting that aquarists use different methods to separate pregnant mollies. And the method you want to use will determine how long you wait before separating the fish. For instance:

1. Using A Dedicated Breeding Tank

This is the most drastic option because you have to move the pregnant molly to an entirely separate tank. This method is more likely to induce stress because the molly has to grow accustomed to a new environment.

Healthy fish struggle with shock whenever you add them to a new tank. Pregnant mollies are more susceptible to shock because they are already stressed. 

It is safer to move a pregnant molly as early as possible in such a case. Though, many aquarists have successfully migrated pregnant mollies mere days or hours before their due date.

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

2. Getting A Breeder Box

Breeder boxes are better than separate tanks because they sit inside the community tank. Your pregnant molly doesn’t have to grow accustomed to a new environment. 

The breeder box allows the creature to remain inside the old tank while separating the molly from other fish. When your molly fish gives birth, the fry can run to a lower section to escape the mother if it wants to eat them. 

Moving a pregnant molly to a breeder box mere days or hours before its due date is safer than sending it to a separate tank. However, you cannot keep a pregnant molly in a breeder box for long because it generates too much stress.

That is why you cannot separate the fish early with this method.[5] Either way; I suggest you release the mother back into the main tank the moment it gives birth.

If you like the idea of a breeding box, I suggest considering one like the Capetsma Fish Breeding Box (link to Amazon). It is designed in a shape that allows the molly fish to swim pretty comfortably.

3. Putting A Divider

A divider is almost always the best choice. Whether you use a breeder box or a separate tank, moving a pregnant molly fish induces stress. The best option is to keep the fish in the same tank.

If you don’t want male fish to harm the pregnant female by chasing it for mating purposes, add more plants and decorations. If the plants and decorations are not enough, introduce a divider. It separates the molly fish without inducing stress.

You can protect the pregnant molly from the attention of aggressive males for the duration of its pregnancy. Once it gives birth, you can preserve the fry by moving the mother to the other side of the divider.

Here is an excellent Youtube video that takes you step-by-step through the process of making your own divider. This way, you won’t have to spend too much money on it:


If your molly fish shows signs of pregnancy, including a swollen belly and a dark gravid spot, it is best to take away the companions immediately. That will allow your molly to remain pregnant in a stress-free environment. It will also prevent aggressions coming from the molly fish itself.

When your molly is about to give birth, the next step should be placing a divider. That will allow the fry to swim freely to the other side while keeping them in the water chemistry they are used to.

Removing the mother at this point can be challenging. That is because the fish is highly susceptible to changes. Also, it is hard to know when the molly has done spawning. For that reason, an aquarium divider will be the ideal choice.


  1. https://fishkeepingguide.net/molly-fish/separate-pregnant-molly-fish/
  2. https://kingsoftheaquarium.com/should-pregnant-mollies-be-separated/
  3. https://fishtankadvisor.com/pregnant-guppy/
  4. https://www.petplace.com/article/fish/general/my-fish-gave-birth-now-what/
  5. https://explorefishworld.com/should-you-separate-a-pregnant-platy/