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Can Molly Fish Get Pregnant Alone? (Without A Male)

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I have grown many pregnant mollies in the past. However, one time, my molly fish got pregnant with the absence of a male. To my surprise, a few weeks later, the fish had given birth to numerous fry. As time passed, I gained some experience in this topic and learned how it could happen.

Molly fish cannot get pregnant without a male. A female molly must be exposed to the male’s sperm in order to conceive. However, females can store the sperm in their ovaries for up to eight months. Therefore, the male doesn’t have to be present once the eggs are fertilized.

As we move forward, I will elaborate on how molly fish can get pregnant even if there is no male in their tank. I will also show you how to identify a pregnant molly fish to ensure that your molly is actually pregnant.

Still curious? Feel free to check my complete guide on pregnant molly fish. There, I discussed how to care for pregnant mollies, how long they remain pregnant, how to identify signs of pregnancy, and a lot more.

Can Molly Fish Get Pregnant Alone?

Molly fish are prolific breeders. They can give birth every thirty days. Depending on the fertility of your fish, it may add as many as one hundred babies to your tank each month.

But female mollies cannot conceive alone. They are livebearers, giving birth to live fry, but only after a male fish has fertilized their eggs. The female molly fish cannot get pregnant without a male molly fish.

But what about molly fish that get pregnant in tanks without male mollies or individual mollies that get pregnant despite living alone in an aquarium? Sperm retention is the most prominent explanation. 

Though, as you will soon see, it is not the only factor that can cause pregnancy in lone mollies:

1. Sperm Retention

Poecillid livebearers are exciting creatures because they can retain sperm, giving birth to babies up to a year later.[1] This is true for all poecilid fish, including guppies, platies, and swordtails.[2]

The females store the sperm in special cavities inside the ovaries. Because the sperm is organic, they have to keep it alive using sugar until the female mollies are ready to fertilize their eggs.[3]

This phenomenon is fascinating because it allows male fish to continue reproducing long after they’ve died.[4] The practice makes sense because female fish in species like mollies tend to outlive their male counterparts by at least a year.

Storing the sperm gives the female mollies the best choice of genes. The fact that the male fish will die long before its offspring are born is not bad because molly fish do not raise their babies.

A mother in a molly fish aquarium will eat its young ones instead of protecting them, which is why it is best to separate the mother as soon as she’s done giving birth. Male mollies are just as dangerous. Therefore, their absence won’t negatively affect future offspring.

Mollies can store their sperm for six to eight months. During that time, they can fertilize their eggs to produce fry several times. In other words, you can expect new fry from a molly every month even though the creature is the only fish in the tank.

Can the sperm deteriorate inside the female fish? This is still unclear. Studies on the subject haven’t produced conclusive results. However, you shouldn’t expect your mollies to store their sperm for more than a few months.

As was mentioned at the start, these creatures are prolific breeders. If you have male and female mollies in a tank, they will start breeding immediately, without your direct involvement. 

Most people have to fight to stop their mollies from breeding. Therefore, if a molly fish has sperm in its ovaries, it will use that sperm at its earliest convenience. 

Like guppies, mollies can produce up to five batches of fry after mating with a male molly once.[5] Yet, you have no way of knowing whether or not a female molly has retained sperm. They don’t manifest any specific signs that betray their state.

You won’t know that your female molly has retained sperm until it gives birth. This is why pregnancies catch beginners off guard in female-only molly tanks. They don’t expect female mollies to give birth without a male fish.

2. Conception At The Store

Don’t be so quick to assume that your pregnant molly fish fertilizes itself using stored sperm. If the fish is new, it was probably impregnated at the store before you got it.

Molly fish can give birth every 30 days. However, you cannot conclude that the molly fish has stored sperm simply because it gave birth long after that 30-day window had elapsed.

The creatures have a gestation period of 50 to 70 days. Sometimes, that figure is as low as 20 days. In other cases, it even exceeds 70 days. Therefore, a molly fish you brought home from the store two months ago can still give birth in the absence of a male fish.

3. Crossbreeding

When you say that your molly fish is alone, is the molly the only creature in the tank or the only molly fish in an aquarium filled with fish from other species? People don’t expect lone fish to get pregnant in a community tank filled with fish from different species.

But cross-breeding can occur. Naturally, different types of mollies can breed with one another. For instance, a balloon molly can mate with a dalmatian molly. People do this all the time because they want to create exciting color combinations.

But you can’t breed a molly with a fish from a different species. For instance, you cannot breed mollies with goldfish. That is because mollies are Poecilia, whereas goldfish are Cyprinidae.

On the other hand, guppies and mollies are part of the same family (Poecilia). Therefore, the two can breed. This is more likely to occur in tanks where the guppy and molly do not have fellow guppies and mollies with whom they can mate.

The results of cross-breeding between the two will vary. They may produce deformed babies. Either way, the offspring will be infertile. Therefore, you shouldn’t expect to make other hybrids from the original batch.

Platies are more complicated. People don’t expect them to breed with mollies because they belong to the Xiphorus family.[6] But many aquarists claim they have seen platies and mollies cross-breeding.

Therefore, if you have platies in the tank, don’t count them out. If you have one molly in the tank and it fell pregnant, it could have mated with male platies. 

Guppies are a safer bet since they have a closer relationship with mollies. Female mollies are large enough to carry Molly/Guppy offspring. 

However, You don’t want a male molly to mate with a female guppy. Female guppies are small. You cannot trust them to carry the hybrid fry to term. Generally, you won’t know whether the other species mated with the female molly until it gives birth. 

If you have hybrid fry in the water, cross-breeding has occurred. If the babies look like ordinary mollies, the molly fish either retained sperm or mated with a male molly before you bought it. 

If you can’t tell whether your fry are ordinary mollies or hybrids, take a look at the following Youtube video. It goes through different cross-breeding options, including guppies, mollies, swordtails, and platies:

What Should I Do If My Molly Fish Got Pregnant?

First of all, if your molly fish is doesn’t share a tank with males and appears swollen, you should make sure that it is actually pregnant. Luckily, pregnant molly fish present typical signs, including:

  • The molly fish’s belly will gradually swell. 
  • The gravid spot will become prominent. 
  • The fish will spend most of its time hiding. 
  • The appetite of a pregnant molly will increase. 
  • The fish will become aggressive.

If you suspect that your molly is indeed pregnant, I suggest that you start by adjusting the water parameters. These are considered 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

To measure the pH, ammonia, nitrates, and nitrites, I use the API Water Test Kit (link to Amazon). This bundle will give you the results within minutes and is highly accurate. It also lasts for about eight hundred measures, so it is pretty cost-effective.

I also suggest that you separate your pregnant molly from other fish. This will prevent unnecessary aggression and attacks. Also, once your fish has done giving birth, place a divider in your aquarium to keep the fry safe.

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Conclusions

Female mollies must be exposed to sperm to conceive. However, the fish can store the sperm for several months. Therefore, the male molly doesn’t have to be present in the aquarium once the female’s eggs are fertilized. 

It is also possible that the molly fish was already pregnant when you bought it. The gestation period can last up to 70 days, and sometimes you won’t notice a swollen belly until the pregnancy is advanced. 

Another possibility is that your molly fish got pregnant from other species in the tank, including guppies. Then, you’ll see hybrid fry. These will be sterile, meaning that they won’t be able to reproduce.

References

  1. https://injaf.org/aquarium-fish/beginners-guide-to-livebearers/
  2. https://en.wikipedia.org/wiki/Poeciliidae
  3. https://www.nationalgeographic.com/animals/article/sperm-hoarders-why-animals-store-semen
  4. https://www.sciencedaily.com/releases/2013/06/130612133403.htm
  5. https://lifeoffish.com/how-long-are-mollies-pregnant-for-12-things-to-know/
  6. https://fluffyplanet.com/can-mollies-and-platies-breed/