Can Guppies Change Their Gender?

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No, guppies cannot change gender, this is the short answer, however, we obviously cannot end the article here since the topic is more complex than that.

The problem I’m seeing is that there is a lot of conflicting information online regarding guppies’ sex differences and sex change. Some claim guppies can change sex, while others that they don’t. As a novice, you can easily get confused by all of it, which can lead to you making poor decisions for your guppies based on factually inaccurate information.

So, let’s clear the air on the topic, shall we?

All Guppies Are Born Females?

No, they’re not. The fact that many people believe that guppies are all born females is only an indicator of the lack of visual differences between young male and female guppies. Guppy fry all look the same, and they all look, females. They all have bland colors and have no visible genitalia or any other indicators to help you determine the gender.

This can cause confusion and lead many to believe that young guppies are all females when that’s not true. That’s why, when guppies grow and males begin to grow differentiating features, the same people go, “There you go, those females are now turning into males,” when reality is a lot simpler than that.

Females didn’t begin turning into males. They were males all along, it’s just that you couldn’t tell. There, mystery solved.

When Can You Sex Guppy Fry?

The ideal moment to sex your guppy fry accurately would be when they’re 4 weeks of age. Some minor differences between the genders may be visible prior to that timeframe, but they may be more difficult to pinpoint. They will become more obvious when the fry reaches one month, and males will grow more distinct body shape and coloring features.

So, don’t worry if your guppy fry looks like females. As a side note, some guppy males display delays in their developmental phase. This may cause them to appear similar to females for longer than other males. So, you have that as well.

Male vs. Female Guppy – How to Tell the Difference?

The differences between male and female guppies are very subtle at first, but they advance pretty fast. By the time the fry reach 4 weeks of age, it’s pretty clear which is which. Several indicators will help you differentiate between the sexes:

  • Body shape and size – Females grow larger than the males and display bulkier and rounder abdomens. Male guppies, on the other hand, are smaller and more slender-looking. On average, guppy females can reach 2.2 inches, while males only settle for about 1.2 inches. Males may also display larger and richer tails.
  • Color and pattern variations – Typically, males are more colorful than the females and will display richer patterns on their bodies, fins, and tails. This is part of their evolutionary prerogatives. Males use their colors to attract females and increase their chances to mate. Females don’t need such a perk, which is why their coloring is rather dull; they instead rely on pheromones and body language to make their intentions obvious. However, not all guppies fall into this category. In some guppy species, the females will also display vivid coloring and pattern variations, blending the gender differences from this perspective.
  • Differences in dorsal fins and tails – Males display larger and fluffier dorsal fins that move with the water currents, while females’ fins are smaller and less flashy. Tails also differ, as males display larger and longer caudal fins, while the females’ are shorter and less imposing.
  • The anal fin – Males have longer and more protruding anal fins, displaying a pointy end. During the impregnation process, they will use this fin to deliver sperm into the female. The female’s anal fin is smaller and in a somewhat triangular shape.
  • The gravid spot – Only female guppies display a gravid spot since, obviously, only females get pregnant. The gravid spot is visible towards the tail in the underside area of the fish’s abdomen. It’s simply a darker area that will grow larger and blacker as the moment of delivery approaches.

These indicators should allow you to differentiate between guppy males and females easily. With time, you will find it even easier to pinpoint them accurately, eliminating any confusion in the process.

Are Guppies Hermaphrodites?

No, guppies reproduce sexually. You need a male and a female to obtain viable fry. It may seem weird that people would ask such a question, but it’s actually justified due to one of female guppies’ evolutionary features. Male and female guppies may not always be around each other in the wild. Because of that, females have developed a unique reproductive feature allowing them to store the male(s) sperm in a special area inside their bodies.

The females will then use that sperm every week to self-impregnate and will keep using the sperm reserves for up to 10 months. Some claims exist of female guppies producing fry with no male present for more than a year. This can cause some people to conclude that females don’t require a male to produce offspring or even that guppies can change their sex on a whim.

As I’ve explained, neither of these beliefs is true.

Do Water Parameters Affect Guppy Gender?

For extensive clarifications on the subject, I will divide this question into 2 parts, each with its relevant corresponding response:

Do guppies change gender when water parameters change? – No, both young and adult guppies will retain their native genders no matter how their environment changes.

Do water parameters influence the gender of the future fry? – There’s no definitive answer to that. We know that various species of reptiles and amphibians will react to their environmental parameters, which will influence the sex of the offspring. But we haven’t observed the same for guppies. Some studies suggest that higher water temperatures will produce more males, while colder waters will produce more females, but take it with a grain of salt. The studies are not conclusive.

So, don’t rely on changing water parameters to influence the fry’s gender. Not only there is little evidence that it works, but you may also hurt the pregnant females in the process.


To dispel misinformation and myths once and for all, guppies cannot change sex and are not hermaphrodites. Females need males to fertilize their eggs and produce offspring, but they will also store the males’ sperm several months for when males are not available.

As a closing note, don’t be worried if all your guppies look like females during their fry stage; that’s normal. You should observe them developing gender-specific characteristics soon, with most becoming more visible when the fry reach their 4th week of life.

Updated: January 20, 2022
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