Can Guppies Change Gender? (Quick Read!)

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In recent years a number of reports have appeared online from people claiming their guppies have changed gender. Drawing on 30+ years experience of with these beautiful fish, I can categorically confirm guppies DO NOT change gender

Since the 1960’s guppies have been a firm favorite in the freshwater fish keeping hobby. Guppies are easy-going, colorful, and hardy. It is easy to see why guppies appear on the list of the most popular fish year after year.

I have been keeping and breeding guppies for 30 years. Over that time literally, thousands of guppies have passed through my fish room. I have enjoyed breeding guppies both for fun and for profit.

Why Do Some People Think Guppy’s Can Change Gender?

I firmly believe that people think their guppies change gender because they see an immature male suddenly color up giving the impression it has gone from being female to being male.

I haven’t been able to find any credible scientific research which confirms guppies are able to change gender.

How To Tell A Guppies Gender

One of the best things about guppies is that it is relatively easy to tell which fish are males and which fish are females. With that said, if you are new to guppy keeping you need to know what signs to look out for.

We can use the following to distinguish males from females;

  • Coloration
  • Size
  • Body shape
  • Reproductive organs


Generally speaking, male guppies are more colorful than females. Traditionally female guppies are bronze to silver color with some coloration in the tail. In recent times, however, some breeders have been breeding female guppies that are almost as colorful as the males.


As well as having more color than the females, male guppies tend to be a lot smaller. A male guppy will reach 1” to 1.5” whereas a female guppy can easily reach 2.5” or more. I recently had a female guppy that was easily 3” long, and maybe a bit larger.

Body shape

Male guppies are built for speed. They are slender and built for darting in and out in pursuit of the females. Female guppies on the other hand are much bulkier. Females spend the vast majority of their time pregnant, which means they often have a swollen belly.

Reproductive organs

Probably the most reliable way to tell a guppy’s gender is to look at the analfin. Male guppies have a more pointed analfin. Females have a very much more rounded analfin. Males use their pointed analfin to fertilize the female guppies.

Do Any Other Livebearers Change Gender?

There are many reports online, especially on forums, of people claiming their Swordtails changed from female to male. Swordtails do not change gender either.

In the case of Swordtails, the dominant male has the longest sword on his tail. Other males in the same aquarium will often hold back developing their swords so as not to be challenged by the dominant male. If the dominant male dies, or the fish keeper removes it from the aquarium, another male will become dominant and his sword will quickly develop. To the untrained eye, this sudden change can appear as if a female Swordtail changed into a male.

I have written more about swordtails changing gender in this article

Do Any Fish Change Gender?

There are some species of fish that can actually change their gender. Clownfish for instance are all born male. Their school is built on a hierarchical system with a single dominant female at the top. When that female dies, a male becomes dominant and changes into a female.

Wrasses, moray eels, and some gobies are also known to have the ability to change gender.

In Conclusion

Guppies and platies are both hardy, peaceful fish that work really well in the community aquarium setup. Putting the 2 species together will create a tank that is full of color and movement. Both species will reproduce on a regular basis meaning there is always something new to enjoy in your tank.

About the Author

I’ve been keeping, breeding, and showing tropical fish for nearly 30 years. Over that time I’ve done it all! I’ve had great success and I’ve made some really foolish mistakes (like the time I bought an Asain Walking Catfish). Read more…
Richard James