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

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Realizing that your molly fish is pregnant can be exciting. But before you get too excited, it’s important to know some of the signs that your fish is about to give birth. This will allow you to adjust the environment in time and possibly get some irreplaceable pictures.

These signs indicate that a molly fish is about to give birth:

  1. The gravid spot will turn deep black.
  2. The molly’s belly will take on a square shape.
  3. The molly fish will go into hiding.
  4. The pregnant molly will start eating less.
  5. The anal vent will become larger than usual.
  6. The molly will shiver and breathe heavily.
  7. The molly fish’s poop will turn white.

As we move forward, I will take you step-by-step through the process of identifying pregnant molly fish that are about to give birth. Then, I will show you what you should do to ensure your molly delivers in a suitable environment.

Also Read: Pregnant Molly Fish 101

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

Pregnant mollies are going to manifest certain signs. That includes a black spot near the anal vent, swollen stomach, and relatively aggressive mannerisms. 

But it is essential to identify the specific period during which the fish will give birth. The information allows you to move the molly to a breeding tank before it’s too late, assuming you want to separate the pregnant mollies from the other fish in a community aquarium.

Admittedly, you cannot predict the exact date the molly will give birth, especially if your molly was already pregnant when you bought it. If you know the gestation period, you could estimate the week in which the fish will drop the fry with mild accuracy. Mollies can produce fry every 28 days.

But the creatures can also remain pregnant for as long as 70 days. It depends on the type of molly fish and the conditions in the tank. If your mollies have given birth before, you probably have a clear understanding of their gestation period.

Therefore, you can determine when the molly fish will give birth by simply counting down the days from the moment you observe signs of mating activity between male and female mollies. 

Because a male fish can take several days to inseminate its female counterpart, your estimate could be off by several days. 

But you can increase the accuracy of what is essentially an educated guess by looking for the following signs. They appear when the fish is about to give birth:

1. The Gravid Spot Turns Deep Black

The gravid spot is a mark that reveals the location of a fish’s womb. It appears near the anal fin, and it will grow darker as the fertilized eggs in the molly fish hatch into living fry and as those fry develop.

The gravid spot should be darkest when the creature is about to give birth because the fry are as large as they can get in the molly’s body at that point. 

However, this doesn’t happen in every case. With some mollies, the gravid spot is darkest during the earliest stages of the pregnancy. It grows lighter over the days and weeks as the abdomen swells, causing the skin to stretch.

2. The Belly Will Take On A Square Shape

The molly fish will start to swell several weeks before it gives birth. Again, like the gravid spot, the size of the molly’s belly will grow in response to the development of the fry.

As the female fish approaches its due date, it will grow so fat that it may look like it wants to explode. At that point, the womb has stretched as far as it is ever going to stretch.

Fish can swell for other reasons besides pregnancy. But if your mollies are truly approaching their due date, the area below the gills will take on a square shape.[1] 

If your molly’s outline is square, it will drop fry within the next seven to ten days. Though, in the presence of poor conditions, it could delay the birth, holding onto the fry for longer than expected and possibly even reabsorbing them in response to an unsafe environment.

3. Your Molly Fish Will Go Into Hiding

Pregnant mollies are less active. Not only are they more likely to hide, but they can manifest aggressive tendencies if other fish approach their breeding ground. A molly fish on the cusp of giving birth may even stop moving altogether.

It will find a comfortable spot and sit there.[2] But you can only notice this behavior if the fish is out in the open. Rather than occasionally hiding, some pregnant mollies will disappear behind plants and decorations in the days leading up to their due date. They won’t emerge until they give birth.

Some pregnant mollies are particularly aggressive during this period. They will attack anything they come across in the water. You are more likely to see this behavior in tanks that don’t have enough hiding places. 

The pregnant molly will lash out continuously because it doesn’t feel safe. Others are meek, showing little or no interest in their tankmates. It mainly depends on the personality of your fish.

Also Read: Why Is My Pregnant Molly Hiding?

4. The Molly Fish Will Eat Less

A pregnant molly’s appetite will drastically fall as it approaches its due date. This isn’t surprising because many mollies don’t move during the final days of their pregnancy. Unless you sprinkle the meal on top of the fish, don’t expect the creature to go hunting for food in the tank.

5. The Anal Vent Will Seem Larger Than Usual

A pregnant molly pushes fry out of the anal vent. Surprisingly, poop leaves the molly’s body through this same canal.

If you look at this vent twelve to twenty-four hours before the fish gives birth, the anal vent will look slightly larger than usual. Naturally, you can only notice the difference in size if you know what the anal vent looks like on most days.

6. Your Molly Will Start Shivering

Like humans, the birthing process in mollies can be long and arduous. Guppies, close cousins to mollies, have the same problem. They will shiver and shudder because of the contractions. Don’t be too surprised if their breathing becomes labored.

The birthing process can take anywhere between ten minutes and two days. During that period, the molly fish will drop the fry at once.[3] This doesn’t happen every time. A molly may release a few fry, wait for hours (or days), and release more fry. But that happens in extreme cases.[4]

7. The Molly’s Poop Will Turn White

One notable sign of imminent birth is the poop. The pregnant molly will produce white poop a few hours before it drops the dry. Once the fry pop out, the molly’s poop will regain its original shape and color.

Like guppies, stringy white poop in pregnant mollies should concern you because it may signify a parasitic infection.[5] You can treat the fish with medicated food. It won’t affect the pregnancy. 

These signs are only relevant to highly observant individuals. New aquarists are unlikely to watch the tank keenly enough to take note of the white poop. And even if they do, they won’t realize its significance: that the molly fish will give birth in the next 1-12 hours.

Mollies tend to drop fry at night if you’re determined to watch the birthing process. This makes sense because predators are less likely to identify and attack helpless molly babies in the dark. 

What Should I Do If My Molly Is About To Give Birth?

First of all, you should know that predators will quickly eat the molly’s fry. That even applies to the parents themselves. For that reason, I suggest separating the pregnant molly from other fish in your tank.

Also Read: When To Separate Pregnant Molly Fish?

Instead of removing the pregnant molly, it is better to remove her companions. That is because putting the mother in a net could cause stress that will harm the pregnancy. If you thought about a breeding box, it is probably too late at this point.

I also recommend that you introduce as many hiding spots as you can. I personally got the MyLifeUNIT Artificial Seaweed Water Plants (link to Amazon). I chose those because they are relatively high, and the fry love to hide between the stalks.

When it comes to the water parameters, these are ideal 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

You can quickly test your water with the API Water Test Kit (link to Amazon). This bundle will measure the ammonia, pH, nitrates, and nitrites within five minutes. It also lasts for eight hundred measures, making it highly cost-effective.

If the toxins are too high or the water is too acidic, make more frequent water changes. At this point, when your molly is about to give birth, I suggest replacing 15 to 20 percent. It is better not to stress your molly with a drastic change, even though it means the water parameters won’t be ideal.


You can tell that your pregnant molly is about to give birth by watching its behavior and appearance. Mollies that are close to their due date will go into hiding and avoid eating. You may also notice shivering and heavy breathing.

At this point, it is best to remove the tankmates and introduce some hiding spots. That will keep the fry safe from predators, including the mother herself. I also suggest that you test the water parameters to ensure they are ideal for molly fish.