How Long Are Molly Fish Pregnant For? [Care and Breeding]

Before coming to the point “how long are molly fish pregnant for“, we should understand their typical behavior, tank conditions and habitat, tank mates, what to feed them during pregnancy, how to breed molly fish, and a lot more.

Bellow is their complete care guide from purchasing them from the pet stores to breeding them in your tank. Happy scrolling…

So many people will have seen a molly fish at different angles. Molly fish are one of the most popular and highly kept fish amongst the fish-keeping enthusiasts.

The molly fish are easy to care for. They are perfect for those people who are new to the fish keeping hobby.

As a social, active and friendly group, you will notice a lot of unique personalities and interesting behaviors start to develop. In a simple way you can add some beautiful molly fish to your aquarium.

As it was classified originally, the genus mollienesia or mollie has some of the most unusual and beautiful varieties of live-bearer fish. One of the most exotic fish available of any genus is the sailfin molly.

Molly fish are available in a number of varieties with different shapes, sizes and colors. With a lot of fish to choose from there is one to suit each and everybody.

In this article, we will cover the most popular varieties of molly fish as well as explaining their care, preferred diet, ideal setups, pregnancy and a lot more.

Care Level:Easy to Care
Temperament:Very Peaceful
Color Form:Various
Lifespan:Up to 5 Years
Size:Up to 4.5 Inches
Minimum Tank Size:10 Gallons
Tank Set-Up:Planted Freshwater Tank
Compatibility:Peaceful Community Tank
Molly Fish Facts and Stats


Molly fish are freshwater fish. It is from the genus Poecilia, in the Poeciliidae family. Except for Endler’s livebearers, all the species in this genus are mollies.

Presently there are 40 species belonging to this genus, and out of 40 species 39 of them are mollies.

These fish are native to the Americas. However, their habitat can differ significantly.

One interesting fact about mollies is that they are livebearers like the guppies.

It means that they can keep their eggs inside their body and they hold the eggs until they can give birth to live young mollies straight into the water.

They are the most popular fish group. A lot of species are easy to care for and hardy, making them perfect for beginner fish keepers.

They perform well in peaceful community tanks.. A group of mollies will thrive and can live up to a maximum of 5 years if kept in a healthy environment.

Mollies are one of the most wanted freshwater fish. It’s rare that you will find a fish store that doesn’t sell molly fish.

Though the rarer species cost more, common varieties could be found for $2 to $4 per fish.

Typical Behavior of Molly

Most of the time they are a peaceful bunch. However they can become aggressive when surrounded or crowded by other aggressive tank mates. So, it’s necessary that their tank is sufficiently big, and that they are surrounded by suitable tank mates (more on this topic later).

Mollies are social and highly active so they enjoy schooling together. Since the males are known to stress and harass females, a shoal should predominantly be female.

Spotting personalities in active fish like these are not so difficult. As you notice their individual differences, watching mollies for a moment will quickly get you attached.

Molly Fish Appearances and Types

How long are molly fish pregnant for?
How long are molly fish pregnant for?

There are so many varieties of molly fish – a few of them are very similar to the common molly fish (Poecilia sphenops). The major differences are patterns and their colors, but shapes and sizes can differ too.

The molly, which are common in nature, has a flattened body. It narrows towards a point at the mouth and is tall in the middle. At the opposite end is the caudal fin which is a big sized fan that can be colorful or transparent .

As a fan the dorsal fin can be raised, flatter against the body, or resembling the caudal fin.

Sexing the molly isn’t too tough and they are easy to mate. The females possess an anal fin that spreads into a fan, but a male’s anal fin is pointier. Females are larger than males. They potentially reach 4.5 inches. The males grow to 3 inches maximum.

Pregnant females will look even more larger. Their bellies swell to be larger as compared to other females.

Here is a summary of some popular mollies for home aquariums:

Black Molly Fish

Virtually these fish are the same as the common molly fish. Apart from that, they’re black all over.

Sailfin Molly

This variety of molly is bred in a lot of various patterns and colors. Their most distinctive feature is their big dorsal fin which is taller. It runs from behind it’s head to just before the caudal fin.

Lyretail Molly

Unlike the sailfin molly fish, the lyretail stands out because of their fins. However this time it’s the caudal fin. The bottom and top of the fin narrow into points and it trails behind the rest of the fish.

Other popular mollies include the Balloon, Dalmatian, White, Orange, and Red.

Tank Conditions and Habitat

A molly’s habitat can vary in the wild environment. So many different water conditions are adopted by them, including high hydrogen sulfide levels and tolerance to brackish waters.

Mostly they are found in the shallow parts of streams and rivers across South and NorthAmerica. The substrate will be sandy with debris and rocks sat on top.

Also, the plants would be plentiful, they’re important for reproduction. Basically they use the plants as shelter butas as well. The rivers are in tropical climates. Therefore, they get a decent amount of light for the growth of plants.

The waters would be slow moving and warm. The water pH tends to be slightly alkaline.

Tank Setup

The mollies that are bred in captivity for the purpose of aquarium trade are used to similar environments as a whole. Therefore you should not worry about each variety requiring a different setup.

A sandy substrate layer along the bottom of the aquarium is a nice idea. While they will not spend a lot of time down at these bottom levels, the fine-grains would be good for keeping your plants.

Taller plants like Anubias nana make a nice shelter for those mid-level swimmers. You are free to select your favorite plants. You can also use decorations like rocks to create crevices and caves. These decorations are very useful for all fish to get away from others where there is a chance of harassing them.

This type of tropical fish needs a heater in the aquarium to maintain perfect temperatures between 72 78°F. Maintain the water hardness between 20-30 KH and pH between 6.7 and 8.5.

Many people suggest slightly brackish waters for the mollies. However, the usefulness of this is not confirmed. It limits the number of tank mates you can keep with them. Therefore we would avoid this recommendation.

For your mollies, standard aquarium lighting will be sufficient. Any other special equipment is not necessary (like an air/water pump) either. These creatures are used to slow-moving water which the outlet of the filter will provide.

What Size Aquarium Do Mollies Need?

At least a 10 gallon fish tank is required for molly fish. A 10 gallon aquarium would be suitable for up to four mollies depending on their species – a 30 gallon tank will be needed for larger mollies like the sailfins.

Every additional molly fish will require approx 3 gallons to live comfortably.

Tank Mates

Since mollies are peaceful species they don’t cause so many problems. Therefore they go great with different peaceful species in a community tank.

Some best choices include: Dwarf Gourami, Corydoras Catfish, Zebra Loaches, Cherry Barbs, Danios, Harlequin Rasbora, Platies, Tetras, Yo-yo Loaches, and Rosy Barbs.

Most of the little peaceful community fish will be good. There are lots more fish to choose from.

From my personal experience, I suggest you avoid aggressive or large fish. Aggressive fish may attack and stress your mollies to the point of death and large fish will try to eat them.

Cichlids are a group which contains so many bad examples. For example, Convict Cichlids have an aggressive nature and they don’t play well with other community members. However, some cichlids don’t create any problem though, like the Angelfish.

A lot of invertebrates will be happy living with your mollies. Mostly they’ll be ignored. Shrimp and snails are popular options, and there are numerous options to choose from.

Keeping Your Molly Fish Together

Keep your mollies in groups of at least four or more, they naturally stick to each other. In the group, the majority of the fish should be females since male mollies are known to harass them. Typically, reproduction is the only reason for aggressive behavior.

What To Feed Your Molly Fish

As omnivores, there are numerous types of food that you can feed your mollies. In the wild environment, they consume small invertebrates, but mainly algae and plants. There are lots of similar foods to provide them in a tank.

Algae plays a vital role in their diet. Mollies use their lips to scrape algae from the surfaces. You can provide them with green vegetables cut into small pieces from your kitchen. Because vegetation is very important. Zucchini, lettuce, and spinach are all perfect options to drop into your fish tank. Also, you can utilize them to make your own homemade fish foods.

Foods like artificial pellets and flakes are an easy option. To provide a wide variety of nutrients try to supplement these with other food options .

Frozen and live foods are perfect sources of protein. Brine shrimp and bloodworms will be accepted happily, but a lot of other options work well too. Providing live foods is very interesting for your fish come feeding time too.

Feed your mollies small amounts twice a day. It will give the digestive system a chance to process the consumed food. Provide them with food as much as they can finish within two minutes.

Molly Fish Care Guide

Mollies are more adaptable and some of the most hardy fish out there.

Unlike any other fish, a clean aquarium is the big thing. You should know how to clean a tank effectively. It includes observing the tank water conditions and checking that nitrites and ammonia are at 0ppm.

This species may develop a situation called “molly disease” (or “shimmies” or “livebearer disease”). As these diseases are caused by poor water conditions, it can’t be termed as a disease.

Affected fish will shimmying and wiggling in one spot and swim around less. Regularly check your tank’s water parameters and rectify any issues, once the water conditions return to normal you will notice improvements in the health of the mollies.

Apart from the molly disease, they can get a variety of diseases which is common in a lot of freshwater fish, such as velvet and ich. Observe your fish very closely to find signs of disease.

Some common signs are: wounds and color changes, spots, a loss of appetite, and inactivity.

Switching up their diet and cleaning your aquarium are a couple of easy ways to minimize the intensity of molly disease. If the issue continues, there are treatments that you can buy from pet stores.

How To Breed Molly Fish

Mollies belong to the livebearers species, meaning they develop their eggs inside their body so that they can release live fry. They are one of the simplest and easiest fish groups to mate regularly and which can be bred in captivity in a simple way.

Conditions in a breeding aquarium should be clean and need to be perfect, the tank (and water in general).

To initiate mating, raising the temperature of water slightly could help, but don’t raise the temperature higher than 78°F.

A courting display is performed by Males for the females. The female will allow the male to fertilize her eggs when she is ready to mate. Many times the male molly tries to “sneak-copulate” where it approaches an unaware female from behind.

Often the females prefer to mate with the males which are large enough.

After the fertilization process is over, it will take upto 35 to 45 days before the young are mollies are released. Large sized females can easily release up to 100 juveniles.

The juveniles are required to be separated from the adult mollies or they will get eaten by the adults. One easiest way is to arrange a breeder’s box and put your pregnant mollies there before they give birth; the juveniles are free to leave the breeder box through small holes but the adult mollies stay trapped there.

Foods like broken flakes can be offered to the young until they’re mature enough to eat the exact foods as the adults. In this situation they could be mixed back in with them.

How Long Are Molly Fish Pregnant For?

Molly Fish Giving Birth

Fish kept in aquariums differ in the way they reproduce.

Huge numbers of the species lay eggs. They hatch into juveniles, with the eggs either blown into bubble nests such as betta fish, bred in the mouth of mother’s with the help of mouthbrooders like cichlids, or even on aquarium plants or in caves.

There is a class where mollies fall off of livebearers that give birth to live fry. Typically, sometimes you will hear fish keepers saying that their fish is pregnant, although the most appropriate word is gravid.

It is said that, it could be quite challenging to know if your fish is gravid, especially if you are an inexperienced person keeping livebearers. But, mollies are ‘cream-of-the-fish-hard’ to tell when they are pregnant, particularly , during the first few days of pregnancy.

The pregnancy duration of a molly fish is between twenty (20) to forty (40) days varying between different species and fishes.

A healthy female molly fish will give birth anywhere from twenty (20) to 100 babies with each pregnancy cycle. They can continue to breed for between 2 and 2.5 years. The average lifespan of molly is 3 years.

Then, how do you know if your molly fish is pregnant or gravid?

Following are some primary signs your Molly will show while pregnant. I have seen these classic signs of pregnant molly fish in my aquarium –

  • Your mollies might become highly aggressive to their tank mates, especially those tank mates that venture into her hiding caves or spot.
  • A pregnant molly will show behavioral change. They tend to hide more than is normal. They only come out to feed and typically they become slower.
  • The gravid spot will get darker and bigger as the fish nears the moment to give birth. So if it is visible clearly, then the molly fish is nearly ready to release its babies.
  • A gravid molly fish will also have a relatively rounder, full-bodied shape.
  • The stomach of pregnant molly fish will particularly grow bigger and seem stretched out.
  • On lighter colored mollies, as their stomach stretches out, you might even be able to notice the eyes of the fry through the belly.
  • A dark triangular spot can be seen near a pregnant molly’s anal vent known as the gravid spot. However, remember that the spot might be quite challenging to discover individuals with darker colors such as black mollies. In this case, you may just have to depend on some other signs to be sure.
  • A black line is also developed by mollies on their bellies; and this will also not be visible in case of black mollies.

How Long Does It Take Molly Give Birth

Usually mollies are pregnant for a period of 20 to 40 days (average 30 days). Certainly, it would be how long mollies will last from the period of conception to birth.

However, prior to this period, there is generally a period called courtship period between the males and females, which will last for a few additional days.

Generally, the period of courtship is characterized by a number of chases every now and then. Quite often it is accompanied by smooth displays of aggression.

This process of dance only ends with the starting of breeding, after that it is followed by the said period of 30 days (on average). In this period the female molly carries her eggs in her stomach up to when she gives birth to live juvenile ones directly into the water.

How To Tell If Your Molly Fish About to Give Birth

Molly fish will show a lot of behavioral change (as we discussed earlier) throughout their gestation period, although a few will be apparent closer to the ‘day of birth’ than the others.

The behavior change of your fish will start from the moment of breeding, sometimes from the period of courtship, then escalate as it gets closer to the time of releasing the babies straight into the water.

However, when the gravid spot of the female is visibly large and dark it is the clear indication that your molly fish is ready to give birth, and the eyes of fry are clearly visible via the translucent stomach edged close to their gravid-mark.

At the same time, but a little earlier, Molly will also get rounded with her belly visibly big from the eggs she is carrying inside her stomach.

You will be able to see her bulge (V-shaped) below the gills and also her outline becomes nicely square around this area before a few days the molly gives birth. It happens along with the gravid area changing in its size.

How Your Mollies Act Before Giving Birth

It is very hard to assume whether a molly fish is pregnant or not. However, as we have seen, there are a lot of clues you can look out for. Some are behavioral, while others are physical.

Since we’ve discussed broadly the physical signs of pregnant molly above, now let’s take a quick look at the behavioral clues of molly.

For beginner fish keepers, almost every tropical fish kept in tanks gets aggressive during the period of breeding and mollies are no exception.

But, you will notice one thing in your aquarium that mollies hide more as they are opposed to getting into a confrontation with other tankmates. Typically, the process of hiding is more apparent closer to your fish giving birth.

So, it is necessary to ensure that there are numerous decorations and plants in your aquarium for your fish to get a hiding spot when it’s time to breed.

From my personal experience, I can say that mollies prefer hiding in dark areas in the aquarium as opposed to well-lit spots. I have also observed that they feel more comfortable and secure in that particular setting.

It is highly recommended to separate your gravid molly from other adults to offer specialized care and treatment. Again, you have to make sure that she does not get stressed out.

Additionally, this will help you to feed your molly more effectively and comfortably without any stress of other tank mates, which can swim faster than your pregnant molly.

Molly Fish Babies

Since we know mollies are livebearers, same as least killifish, platys, and guppies, instead of laying eggs, they release live babies straight into the water.

Sadly, the new born babies do not get perfect parental care from their mother. They are likely to be eaten by their parents as well as by other fish present in the aquariums.

So, you have to provide them parental care if they have even the very little chance of survival.

Once the mother has released her babies, a breeder box can help you keep the molly babies safe. Placing the female molly in a breeding aquarium away from the rest of the community also goes a very long way.

In order to remove the mother from the breeding aquarium once she has released her babies, you can also use a net. A breeding box is less tasking to use and more effective.

As and when the fry are released, automatically they will fall into a seperate compartment away from their mother, where you can easily keep the prey until you catch and shift the adult mollies into the main aquarium.

You can move the molly babies back to the main tank once the babies are mature enough and they can fend for themselves, but ensure that there are sufficient plants for your fry to hide in.

Some other things which play a crucial role to master when caring for your little molly are aquarium feeding and maintenance.

Ensure that the quality of your tank water remains safe by regular water changes. Provide soft food to your little molly in small pieces that the fry can easily consume.

FAQs on Molly Fish Breeding

What does a pregnant molly fish look like?

The belly of a female molly fish will swell to be much bigger than usual. Usually, it is easy to spot, particularly while comparing them to other molly fish residing in the aquarium.

What do molly fish babies look like and how do you care for them?

With large black eyes, the new born molly babies look like a small version of an adult. Depending on the species, colors will vary. Keep your juvenile molly separated from other tank mates (including their parents) until they become mature.

Do mollies eat their babies?

Yes, mollies eat their babies. Including their babies, the mollies feed on almost everything offered to them that fits into their mouths.
In such a situation, a breeder box is highly recommended to use, and shift the adult once the mother has dropped all her babies into the water.

Are mollies aggressive?

Usually, mollies are not aggressive in nature, they are mostly peaceful species. But when overcrowded they feel threatened, and this creature will become highly aggressive.

How long are molly fish pregnant for (Summary)

After a gestation period of 6 to 10 weeks, molly fish will produce a brood of almost 20 to 60 live young.

In a home aquarium, molly fish could be easily bred and they are often already pregnant while bought at a pet store. They are very peaceful in nature and live well in a community tank.

This creature is bred using an internal fertilization process. The males inseminates the eggs when they are inside the stomach of the female. The female molly carries the eggs inside her belly until the newborn fish or fry are ready to give birth.

A molly fish’s gestation period is around 60 days. Sperm can be stored by female mollies for months and they can fertilize eggs as often as every 30 days, even without the presence of any male in the aquarium. The female mollies may give birth to 10 to 60 live fry at a single time.

Arguably, mollies are one of the best breeding livebearers. However, your success rearing them mostly depends on how well you manage and prepare for your female mollies’ gestation periods.

In order to get strong and healthy fry, you have to make sure that your fish are in a perfectly cleaned environment. Don’t forget to feed them timely and properly.

What is your most favorite type of Molly Fish? Let us know in the comments section below…


Dibyajyoti Bordoloi is the creator and author of, a third-generation experienced fish keeper and owner of a successful pet breeding farm. He is also a member of the Center for Wildlife Rehabilitation And Conservation (Assam), the Marine Aquarium Societies of North East India, and the Kaziranga Nature Conservancy of Assam.

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