Pregnant Molly Fish: Behavior, Duration, Care & More

The pregnancy of a molly fish needs to be identified and differentiated from simple bloating. This fish comes from the family of livebearers, that do not lay eggs but deliver babies that start swimming the instant that they are born.

The pregnancy in the molly fish can vary from 20 to 40 days, depending on their type, and the number of times they have given birth. The question as to how many babies a molly fish can give at one time, and if they give birth at night will be covered in this article. Being a fish enthusiast myself, I can answer all of your questions regarding the molly fish pregnancy and also the types of fish they can crossbreed with.

Molly fish are common pets when it comes to keeping an aquarium. People tend to find their types and colors attractive and a good addition to the fish tank. They are also livebearers which means that they do not lay eggs, but give birth to baby fish, thus making them fast breeders. Currently, there are more than 14 types of Molly fish known, which vary in size, color, and shape.

 pregnancy molly fish

When it comes to breeding these species of fish, one needs to know how their pregnancy cycle works, and the environment and conditions required for them to grow in number. In this article, I will be helping you identify pregnancy in your molly fish and will highlight the conditions and details of their pregnancy. So, if you are trying to breed your molly fish, you have come just to the right article.

Here are a few of the most frequently asked questions regarding the molly fish pregnancy:

How do Tell if your Molly Fish is Really Pregnant or Just Bloated?

Just like most people owning an aquarium, I used to keep my mollies in the same tank during their breeding seasons. I continued to do so until I figured out that this way the baby fish do not survive and end up being eaten alive by their fellow aquarium mates.

Since molly fish give birth to babies, so these young baby fish are prone to attack by other fish as well as by their own mother. So, it is extremely vital that the molly fish is separated from the community tank when it is about to give birth.

Now the question is, how do I know if my molly fish is pregnant, or is it just bloated? Certain behavioral changes occur in the mother molly fish, when it is pregnant, which I have pointed out below.

  • Less Movement by Mother Fish: The mother appears to be tired and slow as the movement of the mother decreases, and she prefers to stay in one place instead of moving around. The mother starts to float in one place and the only movement if any, observed is swimming back and forth.
  • Isolated Behavior: The mother isolates herself from the rest of the tank mates. She prefers staying away from the populated area of the tank and starts hiding under rocks and plantations of the tank. Some molly fish come to the surface and start breathing at the surface when they are pregnant.
  • Prefers Dark Environment: Pregnant molly fish prefer dark over light, so they tend to move away from light and take shelter under rocks or plantations.
  • Swollen Belly: The most observable sign is the belly being visibly swollen. This varies from newly producing molly fish to those who have given birth many times. The molly fish who are birthing for the first time do not have a significant belly, while the fish who have given birth many times have larger bellies.
Swollen Belly
  • A visible sign of the baby’s eyes through the Belly: Close to the end of their pregnancy, the eyes of the unborn babies can be seen through the stretched bellies of the mother molly fish. This is the ideal time to separate the mother fish from the community tank.
  • Colored Spot on the Belly: A colored spot on the abdomen can be seen in some of the pregnant molly fishes, which darkens in color as the pregnancy progresses.
  • Aggressive Behavior: Pregnant molly fish also become aggressive towards their fellow tank mates and avoid contact with them.
  • Increase in Appetite: In the first 2 weeks of their pregnancies, molly fish eat more than their normal appetite. After 3 to 4 weeks of the beginning of their pregnancies, the mother loses her appetite and eats nothing altogether.
  • Shivering & Contractions: Molly fishes are also observed to shiver when they are pregnant and might raise their tails. This can be observed as contractions that can come and go throughout their pregnancy.

How Many Babies do Mollies?

When it comes to the number of babies that molly produces, there are many factors that contribute to this.

Having experimented myself, with varying conditions, molly fish can give birth to babies over a wide range of numbers. After having given birth, molly fish can become pregnant right after. This condition may continue over the entire mating season and can be referred to as the “permanent pregnancy” situation.

molly fish baby

Isolated Environment: An isolated molly fish has a greater chance of its babies surviving. The pregnant molly fish must be separated from the community tank a few days before it is due to give birth as it gives the mother time to adjust to the new and isolated environment. This way it can produce babies without stressing out about the environmental change.

Tank Size: The size of the tank that the molly fish is being kept in also determines the number of babies that the mother may have. In a 10-gallon tank, a molly fish can give birth to up to 60 babies. However, in a smaller tank, or much less, a fishbowl, molly fish do not produce a lot of babies.

Clean & Better Environment: If the water in the tank is changed regularly, and a safer environment is provided, molly fish produce more babies. It is better to have plantations and pebbles in the tank as this provides privacy for the molly to give birth in dark. Also, the pebbles and plants provide ample hiding spots for the newly born babies to hide from the mother if she gets hungry and eats them.

Number of Pregnancies: When the molly fish becomes pregnant for the first time, they can only give birth to a limited number of babies, as much as 5 to 10, or at most a dozen. When they have given multiple births, their number of fry increases. A molly fish that has given birth many times can produce up to 100 babies. Some molly fish give birth in batches, with a gap of half a week between the two deliveries.

As we can see the number of babies a molly fish can have varies over different factors. At one time, one of my molly fish, separated in a 5-gallon tank, gave birth to around 50 babies. Had my tank been larger than this, and if I had separated the mother a few days before I did, it could have birthed even more babies.

Do Mollies Give Birth at Night?

As discussed earlier, pregnant molly fish prefer dark over light. This is why they prefer giving birth at night. It helps the babies to escape the predators who might prey on their offspring. There are also other reasons why mollies prefer giving birth at night.

Every organism needs a proper environment to thrive and reproduce. For mollies, the temperature and pH of water at nighttime are highly suitable to produce their babies. Ideally, the most suitable temperature for molly fish is 26-28 °C.

The dark environment keeps them hidden from the other fishes that might harm their babies at night, so birthing at night is preferred by mollies. Too much light may also harm their newly born babies so birthing them at night gives them time to adjust to the light as the night turns to daytime. The night also allows the babies to hide in places so that even the mother is not able to find them and feed on them.

What Can Mollies Breed With?

If you want to crossbreed some of your favorite mollies to experiment with, as I did many times, the good news is that you can! Since mollies have different types, colors, and shapes, they appear different from each other, yet they are the same species so crossbreeding is definitely an option.

I have tried breeding large species of molly fish, such as the balloon molly, with other mollies and expected a larger fish as a product. Due to the size of the balloon molly itself, the offspring could not be any larger than either one of its parents. However, interbreeding in molly species can result in different shapes, and colors and you might end up discovering an entirely different breed altogether.

What Can Mollies Breed With

Mollies can also breed with other species of fish only if that specie is very close in resemblance to their own specie. Guppy, Endler’s, and molly are more or less the same when it comes to methods of breeding. They are all livebearers and can be crossbred. However, the offspring of a guppy and molly is sterile and cannot reproduce and increase in number on its own.

It can be observed that livebearers can be crossbred but as in the case of molly and guppy, the offspring is unable to reproduce and cannot be bred further. Also, livebearers cannot crossbreed with the fish that lay eggs, as they are very different species from each other.

The Bottom Line On Pregnant Molly Fish

I am sure that reading this article has cleared many of your concerns regarding the breeding and pregnancy of molly fish. This species of fish is relatively easy to breed and if tended to carefully, can yield a huge population of fish.

I have kept my mollies separate from the other fish during their breeding season and there is visible growth in their number. You can always vary the temperature, pH, and lighting conditions around your pregnant molly fish to monitor changes in their birthing patterns. The more you experiment, the better you will know what environment your fish will breed the best in.

If you find anything interesting and worth sharing, just ping us back. Happy breeding!

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