How to Tell If a Guppy Is Male or Female

Learn how size, shape, & fins differ between males & females

Co-authored by Devin McSween Reviewed by Natalie Punt, DVM

Last Updated: January 5, 2025 Fact Checked

Guppies are popular pets that make attractive additions to your home aquarium. If you’re curious whether your guppies are male or female, it’s easy to determine their sex once they are at least 1 week old. Just examine your fish’s body shape, fins, and coloring. Keep reading to learn all the different spots to check to tell the difference between male and female guppies.

Male vs Female Guppies

Check the guppy's body shape. Male guppies are long and slender while female guppies are rounder and larger than males.
Look at the guppy’s dorsal fin (on top of its body). Males have long dorsal fins that trail in the water; female dorsal fins are very short.
Check for bright coloring or patterns on the guppy’s body. Males are usually more colorful than females and often have spotted or striped markings.

1

Body Shape

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Male guppies have long, slender bodies while females are more round. The body shapes of male and female guppies are very different and distinct. Male guppies usually have thin, narrow bodies while female guppies typically have a rounder body shape.^{[1]
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- If your female guppy is pregnant, her body may look boxy, stuffed, or lumpy. She may grow even rounder as she gets closer to birthing her young.^{[2]
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- Use a magnifying glass to get a better look at your guppy’s shape, size, and coloring as it swims around in its tank.

2

Body Size

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Get an approximate measurement of your guppies to help determine their sex. Female guppies can grow up to 7 cm (2.8 inches). They are often 2 times as long as male guppies, which can grow up to 4 cm (1.6 inches).^{[3]
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3

Coloring

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Male guppies are more brightly colored and patterned than females. Male guppies are typically more colorful than their female counterparts. Males often have bodies and tails covered in orange, blue, violet, green, black, and white spots and stripes. Female guppies are usually duller in color and have less patterning; many females are just a silvery gray.^{[4]
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- Keep in mind that bright colors and patterns don’t automatically mean your guppy is a male. Some types of female guppies are quite colorful, so check out other physical markers on your fish to determine its sex.^{[5]
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- Look at different breeds of guppies online to determine what breed your guppy is, as well as the different coloring and patterns on your breed's tail.^{[6]
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- Male guppies use their bright coloring to help attract female mates.

4

Anal Fin

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Males have long and thin anal fins while females have triangular fins. Look at the size and shape of the guppy’s anal fin, which is the fin located under the fish and before the tail fin. A male guppy has a long and narrow anal fin with a slightly pointed end. In contrast, a female guppy has a shorter anal fin that is triangular.^{[7]
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- A male guppy’s anal fin is called a gonopodium. It contains his reproductive organs, so he uses his fin to deliver sperm to the female.

5

Gravid Spot

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Only female guppies have a dark-colored gravid spot. Check the underside of your guppy’s body, near the end of their belly and above the anal fin, for a dark spot. This is called a gravid spot, which indicates that a guppy is female. Male guppies do not have a gravid spot.^{[8]
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- The gravid spot rests above a female guppy’s “womb,” or where her fertilized eggs develop into baby fish.
- If your female guppy is pregnant, her gravid spot will likely get darker and bigger as she gets closer to delivering her young. As her due date approaches, you may even see the babies inside her, close to her gravid spot. Once she has her babies, her gravid spot will get lighter again.

6

Dorsal Fin

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Look at the shape of your guppy’s dorsal fin, which is located on top of the fish. Male guppies have long dorsal fins that flow in the water as they swim around. Female guppies usually have shorter dorsal fins that do not trail in the water as they swim.^{[9]
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7

Tail Fin

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Check out your guppy’s tail fin (also called the caudal fin), which is located at the end of their body. Male guppies have long and broad caudal fins that are often brightly colored with elaborate patterns. Female guppies typically have shorter caudal fins that are not as wide and long as males’.^{[10]
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Male guppies tend to chase and swarm female guppies, which can be another way to determine the sex of your fish.^{[11]
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To properly care for guppies, aquarium specialist Marshall Stephens recommends keeping 2 female fish for every male fish. He says that males sometimes fight each other when they’re left alone together.

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If you are breeding guppies, remove the male and female fish once the fry are born. Adult guppies sometimes eat their own young.

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Tips from our Readers

The advice in this section is based on the lived experiences of wikiHow readers like you. If you have a helpful tip you’d like to share on wikiHow, please submit it in the field below.

If you see one guppy chasing another, the one that's doing the chasing is almost certainly a male. The male wants to breed with the female, so he will often pursue her in this way.
In my opinion, if you plan to breed guppies, it's best to put 1 male guppy with 3 female guppies so he alternates who he breeds with the females won't get too exhausted.

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