Can Molly and Swordtail Breed? No.

Last Updated on August 3, 2022 by cmoarz

It’s unfortunate that the search engine is so full of autogenerated trash content that it’s difficult to find a decent answer to such important questions. However, the answer is no. Molly and Swordtail cannot breed (at least on their own) because they are too far removed from their mother species.

Mollies (Poecilia latipinna) and swordtails (Xiphophorus hellerii) are both freshwater fish that are popular in home aquariums. They are similar in size and appearance, and both have long-flowing fins. However, they are not the same species and cannot interbreed without help from a laboratory (more on that at the bottom of the article).

Where does the myth that these two fish can breed together come from?

It’s not uncommon for people to look up whether two fish can breed together before buying them for their aquarium. This is especially true for beginner fishkeepers who want to make sure they are getting compatible fish.

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The internet is full of bad information, and this is one of those cases where bad information has been repeated so many times that it has become accepted as fact. If you search for “can mollies and swordtails breed,” you will find many websites that say that they can.

This is likely due to a misunderstanding of how fish reproduce. Many people think that as long as two fish are of the same size and shape, they can breed together. This is not true. In order for two fish to breed, they must be the same species, subspecies, or in some way be compatible for hybridization.

Mollies and swordtails may look similar, and come from the same order, Cyprinodontiformes, but are far removed genetically from each other. They have different numbers of chromosomes, which means they cannot produce viable offspring together. Even if they could mate on their own, their babies would not be able to survive and the female molly would almost certainly perish.

The fact is, This myth came about because mollies hold onto the males’ sperm for a long time after mating. So, if a molly and swordtail are kept together in an aquarium, the female molly may become pregnant and people may come to the conclusion that the two species can breed together when, in fact, they cannot.

Now, that’s not to say these species can never be hybridized

Humans like to do weird things, and one of those things is trying to hybridize different species of animals together. This has been done with mollies and swordtails in a laboratory setting, but it is not something that can be easily (or ethically) done at home.

Mollies and swordtails have been successfully hybridized in a lab, but the process is complicated and expensive. It involves artificially inseminating the female molly with the male swordtail’s sperm. This is not something that can be done at home, and it is not something we recommend trying.

In conclusion, mollies and swordtails cannot breed together on their own. The myth that they can come from a misunderstanding of how fish reproduce and vague representations of labratory data put forth in various papers and books. If you want to learn more about this topic, we suggest reading one of those books or papers rather than trusting the internet.

Happy fishkeeping!


Owner of and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!