Do Guppies Change Gender? (Why Do Fish Change Gender?)

Image of two guppies swimming together

Did you know that nearly 450 species of fish can change their gender? These fish usually resort to a gender change when their population is deficient in one gender. By changing the gender, they replace the missing sex and continue to reproduce. However, all fish don’t undergo spontaneous gender change when they can’t find a mate. So, do guppies change gender?

There are no scientific studies that suggest guppies can change their gender. However, gender change is a common phenomenon in marine fish species. So, like many livebearer fish that spontaneously change gender, it’s theoretically possible for guppies to change gender if the circumstances demand it.

Let’s talk about this in detail now.

Why Do Fish Change Their Gender?

Reproduction is an essential biological trait for living organisms.

Without producing offspring, the future of a species comes under threat.

However, for reproducing and giving rise to future generations, both males and females of the same species should exist.

In an ideal world, this wouldn’t be a problem. Most fish won’t face any difficulty in finding mates.

However, when either of the genders doesn’t exist in a fish population, the members may exhibit protogyny.

This means that an animal that begins life as a female will transform into a male or vice versa.

Interestingly, some fish show sequential hermaphroditism. These fish have both male and female reproductive organs.

They transition from one gender to the other during their life depending on which gender is scarce and required for breeding.

Take the example of the mangrove killifish. It first lays eggs and then fertilizes them.

A similar curious phenomenon is commonly seen in clownfish. All clownfish are born as males. They are considered inactive males.

When it’s time to breed, the largest clownfish in the group changes into a female.

At the same time, the next largest clownfish becomes an active male. They mate and produce offspring.

Now, if the female perishes for some reason, the active male becomes a female, and the next largest inactive male in the population takes over the role of an active male.

They mate and ensure the continuity of the species. Hence, the breeding process is not disrupted.

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How Guppy Genders Differ?

It’s easy to differentiate between adult guppy males and females. There are visible differences in size and color.

Interestingly, these differences become evident only when guppies reach adulthood.

All guppies look alike when they are fry. However, as weeks go by, differences begin to appear.

Hence, it can take more than a month to ascertain the gender of certain guppies correctly.

By the time guppies are four weeks old, they are half an inch long.

You can spot the characteristic traits of the fish at this stage.

This is the right time to determine whether your guppies are male or female.

Here are the different factors that will help you decide if a guppy is a male or female.

  • Female guppies are bigger: Guppy females are larger and longer than males. The difference in size is easily noticeable as male guppies rarely grow as big as females. So, you can differentiate between males and females by comparing their sizes.
  • Male guppies are more colorful: The tail and fin colors of male guppies are vivid and beautiful. They are brighter and pointed. Meanwhile, female guppies have smaller, square fins. They are not as attractive as males and have fewer colors. Male guppies have colorful bodies and tails. Female guppies may have faint streaks of color. However, these colors are usually limited to the tail region.
  • Female guppies have a gravid spot: Female guppies have a dark, gravid spot on their abdomen, near the anal fin. It’s absent in male guppies. The gravid spot indicates the space where female guppies hold their fry during pregnancy. This area will grow in size in a pregnant guppy female and take on a boxy structure towards the end of the pregnancy. It will also become more visible as a guppy grows older.
  • Male guppies have a gonopodium: The anal fin is different in male and female guppies. In male guppies, it’s called a gonopodium. The gonopodium is long and pointed. You can easily identify the male gonopodium in a male guppy by the time it is four weeks old. The gonopodium is the reproductive organ of a male guppy. The male inserts it into the female during mating to deposit sperm into the female’s body. Since guppies are livebearers, fertilization occurs inside the female’s body, and the female gives birth to live fry.

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Why Is It Important To Identify The Gender Of Guppies Earlier On?

Guppies are prolific breeders. They have huge batches of fry very frequently when compared to other aquarium fish.

This aspect makes it very important to separate guppies by gender when they are young.

If you don’t separate male and female guppies before they reach maturity, you can end up with more fish than you would want.

Male guppies are ready to mate by the time they are a month old.

Female guppies mature by three months of age and can give birth at this age. Once they are mature, guppies constantly mate.

Female guppies will continuously become pregnant and give birth.

During the lifespan of a female guppy, she will have nearly twenty batches of offspring.

If you allow the fry to remain in the same tank as the adults, they will contribute to the population.

Before you realize it, your tank will have more guppies than you can count.

So, you may like to separate the two genders before they reach the stage where they are ready to mate and produce offspring.

Keeping them in a single-gender aquarium will help you limit the problem of having more guppies than you can handle.

How To Control The Guppy Population From Getting Out Of Control?

Since guppies are livebearers, they can produce a lot of babies each time.

As a result, the number of guppies in your tank can quickly spiral out of control.

When this happens, it can lead to a resource crunch and a lack of space in your fish tank.

An overcrowded aquarium is also not an ideal living environment for any fish.

To prevent all these problems, you should take suitable precautions to avoid overbreeding of guppies.

The following steps will help you in this regard.

1. Separate the males and females.

Young guppies are bound to appear in a mixed-gender tank. You can avoid this by keeping only one gender in a tank.

Nonetheless, it’s possible that your female guppies are already pregnant when you got them.

As long as you keep only one guppy male with two or three females, you can exercise some control over the guppy population.

However, you should promptly remove the guppy fry and give them away soon after they are born to keep things under control.

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2. Don’t provide hiding places.

When the guppy babies are in the same tank as adult guppies, they are at risk of being eaten.

Adult guppies will eat any guppy fry that get too close and fit their mouths.

However, in an aquarium with several plants or decorations, young guppies survive by hiding from the adults.

If your guppy population seems to grow drastically, remove a few plants and decorations from the tank.

Let nature take its course, and you can expect some control over the guppy population in your tank.


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