Facts About Molly Fish Pregnancy

Molly fish are a striking and beautiful freshwater fish variety for your aquarium. There are many types of Molly fish, such as black, sailfin, Dalmatian, balloon, and lyretail Molly fish. These fish are very adaptable and peaceful, making them a great addition to any fish tank. Molly fish are also easy to breed and usually already pregnant when purchased.

If you have a pregnant Molly fish in your aquarium, you are probably wondering how long Molly fish stay pregnant. You will also need to know how to care for your pregnant Molly and her fries, so keep reading.

How Long Are Molly Fish Pregnant For?

These tropical fish generally stay pregnant for 60 to 70 days, after which they give birth to 10 to 60 fries. Similar to Guppies, Molly fish do not lay eggs; the babies hatch internally before delivery. Molly fish are an ideal choice if you want a live-bearing fish for a community tank. A single Molly fish produces over a hundred babies, called fries, with a single pregnancy.

How Molly Fish Breed

It is best to have multiple female Molly fish with a single male Molly fish. Typically female Molly fish only breed with a single male Molly fish who has the largest fins and boldest colors. Male Molly fish are aggressive to other males, so it is best to have at least two to three females per male in your tank. The males can also stress out female Molly fish because they are always looking to mate. For this reason, it is always better to have more females compared to males in your fish tank.

The fish copulate with the male under the female fish. Successful mating leads to pregnancy and eventually the birth of the fries.

How To Tell If Your Molly Fish Is Pregnant

A pregnant Molly fish isn’t hard to identify and there are clear, visible signs. These signs are easy to spot once you’re aware of them. The longer your Molly has been pregnant, the more apparent these signs become. If you plan to breed Molly fish or have a tank with males and females, it is essential to remember these signs.

Pregnant Molly fish require special care and attention. This is mainly because Molly fish have been known to eat their fry so many of them don’t survive. The three main ways you can tell if your Molly fish is pregnant are:

Physical Changes

Your Molly fish will develop a bulky, boxy appearance rather than her usual soft, rounded body. If it is early in the pregnancy, you might not notice it easily. However, near the end of her pregnancy, your Molly fish will have a distinct square-like shape to her belly. The abdomen can grow significantly since Molly fish can carry up to 120 babies in one pregnancy. The more babies your Molly will have, the larger and boxier her body will appear.

Gravid Spot

It is not uncommon for fish to grow bigger due to eating. The best way to distinguish between growth due to diet or pregnancy is through the gravid spot. The gravid spot is a dark triangular mark located under your fish’s belly. When Molly fish are pregnant, you will notice the gravid spot near their anal cavity.

This dark spot is the cluster of fry contained within her. As your Molly fish reaches the end of her pregnancy, you can even see the babies within her belly. The eyes of the fry are large and prominent and become apparent during the later stages of the pregnancy. This may be more difficult to notice with a black Molly fish. The lighter your Molly fish is, the easier to see her gravid spot.

Behavioral Changes

Pregnant Molly fish will also show changes in behavior such as aggression towards other fish. This doesn’t mean your fish will attack other fish, but they will react aggressively when bothered. They will also try to avoid other fish as much as possible and find hiding spots within the tank. Since the male Molly fish are always looking to mate, a pregnant Molly will often hide to avoid feeling stressed by their pursuit. If two Molly fish breed successfully, these signs can show a week after.


Similar to other animals, a pregnant Molly fish will eat more. While fish are generally hungry and will look for opportunities to overfeed, a pregnant Molly actually needs more food. They need to provide for the fry they are carrying inside. It is best to feed your Molly fish high-quality fish food while she is pregnant. Avoid feeding food that contains too much air or filler. During this time, a balanced diet is essential for the health of your pregnant Molly fish as well as her babies.

Seeking Warmth

When Molly fish are pregnant, they will look for warm spots in the aquarium. You will notice them lingering by the tank’s heater or temperature stabilizer. If you have a UV light in your tank, a pregnant Molly fish may even hover near the surface. This is because the warmth from the light creates warm spots near the surface of the aquarium.

This is because fish prefer to maintain a higher temperature during the gestation period. A warmer tank ensures your Molly fish doesn’t stay pregnant for too long.

Molly Fish Pregnancy Stages

Molly fish pregnancy occurs in two stages: fertilization and gestation. When the gestation period is over, Molly fish gives birth to many fries. These are live fish instead of eggs like other species.

1. Fertilization Stage

In most types of fish, the female lays eggs that are fertilized by the sperm of the male fish. With some species, fertilization occurs within the fish’s body and the eggs are laid after. These eggs hatch and new fish are born. However, Molly fish fertilize and carry the fertilized eggs within their bodies.

Molly fish also have the ability to store the male’s sperm within their body for months. This means they can fertilize their eggs again after a time interval to give birth to new fry. Most Molly fish can fertilize their eggs every 30 days so they can stay pregnant for the long term.

2. Gestation Stage

The gestation stage is when the eggs or embryos develop within the mother’s body. The fertilized eggs develop into fish babies called fry within the Molly fish mother. The gestation stage generally lasts 20 to 40 days among most Molly fish. However, some types of Molly fish, such as the Dalmatian Molly variety, actually gestate for 60 days. If your Molly fish is young or it is her first pregnancy, she will probably give birth to fewer fries than a mature, older fish.

3. Birth

Your Molly fish will get ready to give birth near the end of her pregnancy. The fries are fully developed at this stage, and their eyes are visible through the mother’s belly. If Mollies feel unsafe or uncomfortable, they can stay pregnant for longer and avoid giving birth. It is best to separate your Molly from the other fish when she is about to give birth. A safe, warm tank with enough hiding spots is ideal.

Signs Your Molly Is About To Give Birth

Knowing if your Molly is ready to give birth is important to ensure she has a comfortable delivery with no complications. When your Molly is near the end of her pregnancy and about to give birth, you will notice the following signs:

Gravid Spot Visibility

The gravid spot becomes very visible as the end of your fish’s pregnancy approaches. When your fish is ready to give birth, the spot is the most visible. It is near the anal vent and too large and dark for you to miss.

Hiding Behavior

Molly fish that are close to giving birth will look for hiding spots in the tank. You will rarely see them swimming out in the open with other fish. They will prefer a cozy, warm hiding spot near the heater to give birth. However, it is recommended you separate your Molly fish from the other fish in the tank. This is also because the fries are small enough to be eaten by the mother and other fish. Separating the mother is ideal if you want all the fries to survive.

How To Separate Your Pregnant Molly Fish

You should take water from the main tank and add it to a new tank for your pregnant Molly. If you don’t want to make an effort to set up an entire tank with its own heater and filter, you can also opt for a breeder net that can separate the pregnant Molly and her babies. You can also DIY a breeder box for your fries.

After your fish has given birth, you should move her back into the main tank. If not, she will eat the fry she has given birth to due to their small size. You should separate the Molly fries for at least two weeks. During this time, feed them a high-quality diet to encourage their growth and development. Your fries will be large enough to move to the main tank after two weeks if fed well. After this period, they are too large to be eaten by other fish in the tank.

Low Appetite

Your Molly fish’s appetite will decrease when she is about to give birth. Typically, fish swim to the surface when you feed them. If you notice that your pregnant Molly is hiding and does not swim up to eat, it can be a sign that she is ready to give birth.

How To Care For A Pregnant Molly Fish

Comfort and safety are important for a Molly fish to give birth successfully. Here are some tips and tricks to care for your Molly fish when she is pregnant:

  • Feed your pregnant fish a high-quality diet. This is important for her as well as her babies.
  • Make sure your Molly fish stays warm throughout her pregnancy. Increase the temperature of the tank by one or two degrees. This is especially important near the end of her pregnancy.
  • If you can not afford to move your pregnant Molly fish to a separate tank, make sure there are enough hiding spots. This is helpful because your fish can hide to avoid persistent males that will try to mate with her despite being pregnant.
  • Near the end of your Molly fish’s pregnancy, the ideal solution is to move her to a separate tank. She will need a safe, comfortable, and warm environment to give birth. A separate tank is much better for the birthing process than installing a breeder net.

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