Can A Molly And A Swordtail Breed?


Molly and swordtail are livebearer fish originating from the Poecilia and Xiphophorus family. These two individuals are quite popular in the aquarium hobby and they are especially recommended to beginners. Therefore, people have been raising them for a long-time separately as well as together in the tank. In this article, we would like to talk about these two species and answer one of the most frequently asked questions – can a molly and a swordtail breed?

Molly and swordtail can technically interbreed but it might induce a serious risk of health issues and eventually end up with fatal results. Therefore, it’s not recommended and you should try to avoid this.

The majority of people are not properly aware of breeding facts and techniques when it comes to aquarium fish. There are many species out there and if you are willing to raise several individuals in the tank you should know who can interbreed. Otherwise, you will encounter significant problems that might result in the death of your fish. We are here to provide information regarding these two species. Let’s start!

Can A Molly And A Swordtail Crossbreed?

There are various viewpoints regarding this topic and people are talking about different experiences when it comes to breeding molly and swordtail. Generally, it is considered that these two species are not able to interbreed and if they do, it might cause serious issues. We would like to list some of the reasons behind this statement.

1- Molly And Swordtail Can’t Interbreed

The first reason why it is impossible for them to interbreed is that they belong to different families. Even though they are both livebearer fish mollies are part of the Poecilia family and swordtails originate from the Xiphophorus family. It is a general rule that they can’t cross-breed outside their families.

2- Female Molly Can Die After Being Impregnated By Swordtail

Another reason is that the majority of people have experienced fatal results after the interbreeding of these species. They have noted, that female molly will most likely die after being impregnated by a swordtail. So, it underlines their incompatibility and you should absolutely avoid their cross-breeding.

3- Incompatible Breeding Process

Some people have noticed that one of them got pregnant while being together in the aquarium. This is one more reason why people think they can actually interbreed but we would like to note, that both mollies and swordtails are able to store the sperm for a long time and they get pregnant by using this sperm from the original partner.

As you can see it’s not possible for mollies and swordtails to interbreed. In the next part of this article, we want to describe the process of breeding for both species if you are willing to raise one of them in the tank.

Can A Molly And A Swordtail Breed?
Can A Molly And A Swordtail Breed?

How To Breed Mollies

The breeding process for mollies starts by chasing and displaying specific behavior. It depends on the species but in most cases, male mollies chase females in order to copulate and fertilize eggs. It happens the opposite too and we can often see females chasing male mollies and giving some signs for mating. These signs might be when they go vertical or start swimming slowly hinting males that they have agreed to mate.

Generally, it is recommended to keep one male molly in the tank as it can easily mate with multiple females. It is a good idea to transfer females into separate tanks after mating and they will give birth to fry in a few weeks.

Livebearer fish are relatively lucky compared to others and they have an easier time giving birth to babies. Since the process of fertilization happens inside the female molly and babies come out of the eggs only after that they give birth to offspring. This way, they don’t have to protect their eggs, and fry fish are able to live on their own.

How To Breed Swordtails

Swordtails are livebearer fish as well and they give birth to live fry. The best partner for them is considered to be a male member of the platy family, so it will be good if you mix up these two species. 

Sometimes when your female swordtail is a newcomer to the aquarium it might ignore the presence of the male entirely. You might think that they are not interested or capable of mating but this strange behavior means that it is getting familiar with the environment and she needs some time for that. 

Breeding of Molly and Swordtail
How To Breed Swordtails

When the egg is fertilized it needs approximately one month for offspring to appear. You might also notice that female swordtails start refusing to eat and bury themselves at the bottom of the aquarium. They are able to give birth to approximately 100 fry and like mollies, they can also store the sperm for a long time. Therefore, they will give birth again in few weeks even without male partners. 

When it comes to feeding your swordtails, you should provide insects and plant particles as they are omnivorous species. It is very important for their diet to include live foods and a large amount of meat and also, we would like to highlight that frozen and freeze-dried food works best for them. 

Similarities and Differences of Breeding Process Between Mollies And Swordtail

The breeding process for each individual carries some similarities and differences. Therefore, we want to describe these processes in detail that will give you a better understanding.

As we have already mentioned, mollies and swordtails are livebearer fish which means that their offspring has developed internally and then they give birth to fry fish. The internal fertilization allows female mollies to have eggs inside after the mating and they remain there until fry mollies are prepared.

We can see a considerable difference when it comes to the age of breeding. It mainly depends on the certain type of mollies but generally, females become reproductive after 6 months while males take up to one year. As for swordtails, they don’t need this much time and usually, they are ready to breed when they reach 3 months of age.

The time frame for breeding is similar for both individuals and it takes approximately 1 month for offspring to appear when the egg is fertilized. This is the period when mollies and swordtails are waiting for their fry to become independent and live on their own.  

One more quality they have in common is that female swordtails and mollies are able to store the sperm for a long time and they can fertilize eggs without the presence of the male in the tank.

The process of breeding is quite simple in both instances and you don’t have to interfere. You will notice when male fish will go under the female and the copulation will start. Generally, they will show similar pregnancy symptoms as they will start hiding at the bottom of the tank and refuse to eat anything. Also, their enlarged abdomen will be noticeable.

One major distinguishing attribute is that unlike mollies swordtails often eat their newborn babies. You should pay good attention to avoid this and make sure your swordtails are well fed before they give birth and it will be good if you transfer fry in another aquarium. Also, you can add some decorative plants and create hiding places for fry. It takes approximately 2 months for newborn swordtails to mature and become independent and then you can contain them with adults.

You have to make a proper tank environment for your pregnant mollies and swordtails to feel comfortable including desired shelters and plants to hide and it will be good if you keep the water warm as they feel more relaxed this way.

Complications for Cross-breeding Process Between Mollies And Swordtail

As we have already noted, the first complication for the cross-breeding process we encounter is that they belong to different families. Swordtails are part of the Xiphophorus family and mollies come from the Poecilia family. Due to this reason, it is impossible for them to cross-breed as they are only able to interact with the species originating from their family.

They are coming from different backgrounds and as a result, the structure of their gonopodium is contrasting. Therefore, it does not allow either of them to interact and have a copulation. However, there have been rare occasions of this process, and every time people have experienced the death of their female individual.

The Takeaways

In this article, we have reviewed one of the most popular fish species among livebearer enthusiasts – mollies and swordtails. They are extremely easy to raise in the aquarium and therefore, these two fish are often recommended to newcomers to this hobby.

However, they are not able to cross-breed due to several reasons. They are coming from different families and as a result, their gonopodium structure is not the same. This prevents them to interbreed and if they try it may end up with the death of your female fish.

On the other hand, they carry a lot of similarities in the breeding process and we have described them thoroughly. We hope this article was informative enough for you to properly raise swordtails and mollies in the aquarium.

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