Should Pregnant Mollies Be Separated?

Mollies are one of the most popular fish for aquariums. They are a good choice for new enthusiasts because they are easy to care for. Mollies can come in many varieties and colors, and they all have their characteristics.

Mollies are live-bearing fish and give birth to live young instead of laying eggs. Tank owners may find their Molly offspring under threat, so this bears the question:

So, should pregnant mollies be separated from other fish? When you have a pregnant Molly, you do need to separate them from the rest of your fish. Because Mollies are live-bearing, other fish may think the babies are food. Besides, once your molly has given birth, you need to make sure the babies have protection from their mother.

If you spot your molly has an extended stomach, then there is a chance she is pregnant. This issue with separation is, not knowing when your fish mated. The gestation period can be between 35 and 45 days. If mollies give birth in the tank, there is a good chance other fish or the mother eats the fry.

Read on, and you will learn how you can take care of your pregnant molly and her offspring.

How Can I tell my Molly is Pregnant?

You can find a puzzling time if you have only female mollies, and one ends up pregnant. The females can store male sperm inside their bodies for several months, and this allows them to fertilize eggs as required.

Signs you may spot that your molly is pregnant are black lines on her belly. Black spots close to the anal vent, and she will show some behavioral changes. She may be more aggressive or become isolated and eat more.

When it comes close to the time of her giving birth, you, as the owner of the tank, have a hard decision to make. You either remove your molly into another tank or take precautions, as we will see. Alternatively, you leave her in the tank and see how many baby fry survive if you do not want to breed more mollies.

Mollies, in general, are not an aggressive fish, yet when they are pregnant, they do show aggression and begin hanging around close to your tank heater to stay warm.

Separation of Your Molly from Your Tank

If you decide to keep all the fry and expand the numbers of fish in your tank. There are a couple of ways to do this. Generally speaking, you will need to make sure:

  • The fry are in a safe environment
  • You feed your fry regularly
  • You make frequent water changes
  • You acclimatize your fry to the conditions of your main tank

1# Preparing Your Nursery Tank

Your nursery tank needs to be five to twenty gallons in size. If you are keeping the parent molly with the fry, then the tank will need to be on the larger size. If you are separating, the fry from the mother, then between five and ten-gallon tanks are ideal.

You will need a filter, but as these can suck up the fry, you are better using a sponge filter for this nursery tank. If you have another kind of filter already, you can purchase mesh covers, or you can easily make your own with a piece of nylon stocking and fixing it across the inlet of your filter.

Heating the tank is vital. Temperatures for your fry will be between 72 and 84 degrees fahrenheit. The size of the heater can vary, and generally, you may need around 5 watts per gallon of tank water.

2# Using Your Aquarium

Although you can move the molly away from other fish when she is about to give birth, there are other ways you can keep her in the main tank and still make sure your fry won’t be eaten, and they can stay safe.

Breeder’s boxes are an ideal solution for complete separation. These contraptions sit on the side of your aquarium and protect the fry from other fish once they are born. Besides, there are small spaces at the bottom of the breeder’s box; this allows the fry to swim away from the mother, so even she isn’t able to eat them.

Another way you can care for the new fry in the aquarium is by stocking up on plants. Because they are not for any nutritional benefit, these can be plastic as well as real. One of the more common plastic plants is these plant balls.

Fry can swim into and hid in these clusters of leaves until they are large enough not to be eaten.

If you go for live plants, use ones that have large leaves. These can deliver plenty of cover in the tank corners where the fry can easily hide. It will take around two weeks before you fry can come out of hiding, and they are too large to be eaten.

Tank owners can also choose Java moss or hornwort to place inside their tank.  Java moss might be the most common moss among fish owners because it does not need high water quality or much sunlight to grow.  Hornwort is another plant that can easily grow in a tank without much nutrition. This grows upright, and the tall stems can offer external protection around the fry. This is ideal for aquariums that are five gallons and above.

Using the above methods rather than using a nursery tank is that your fry acclimatizes to your main tank conditions. This can save time and it also does away with the need for setting up and running a separate nursery tank.

3# Caring for Your Fry

Feeding your fry will be a vital step in their growth. You can purchase food that they make specifically for these, or you can take high-quality fish flakes and grind this into powder form for them to feast on. You can also do the same with baby brine shrimp to add more protein to their early diets.

The feeding pattern needs to be several times during the day. If you give a good pinch, this should be sufficient, yet it will depend on the number of fry you have. A molly can give birth to lots of babies in one go.

Any food that your fry don’t eat needs removing. A fine net is the best way to scoop this up before it manages to sink and work its way toward your filter.

Water changes need regularly conducting if you are using a nursing tank. When doing so, you can top up with water from your main tank. This will help introduce them to the environment when you add them in with your other fish.

You need to change around twenty to thirty percent daily. If you are using a nursery tank, then the fry will be around 2-months old before you can transfer them to the main tank. It is easy to see why breeding boxes are a great option for your molly fry. There is no messing, and they are ready to go from day one.


It can be straightforward caring for fry and making sure; other fish don’t eat them when they are small. The most difficult part can be getting the timing right of when to separate your pregnant molly from your other fish.

Once you get this timing right by watching the signs, you then need to decide what to do with all your new fry. The number she can give birth to mean you can find you have a tank that quickly becomes overpopulated.

You can limit the number so males to females in a bid to prevent unwanted pregnancy, although if they can store sperm, it may be too late by the time you cull the males.

Raising molly fry isn’t hard, and as you see from all the above, the only hard part is choosing the best way to separate the mother molly from your other fish, and how to feed and care for the fry once they are born.