How to Determine the Sex of Guppies
If you are planning on breeding guppies, or want to avoid breeding guppies, it's vital to know how to tell the sexes apart. Since guppies are cannibalistic, and the males are more colorful than the females, some aquarium hobbyists prefer to keep only males. The easiest way to sex guppies is by looking for the male's sexual organ, the gonopodium. The gonopodium is a modified anal fin the males use to inseminate the females.
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Instructions
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Examine the anal fin. Female guppies have rounded anal fins, while the males have pointed anal fins.
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Look for a gravid spot. The gravid spot is a black dot in front of the female's anal fin. Females begin to show a gravid spot at around one week of age. Males don't have a gravid spot.
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Look at the shape of the body. Females have boxy, rounded bodies that get larger when they are close to giving birth. The body on the male is more slender.
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Examine the tail. The shape and color of a guppy's tail depends on the variety, but in general, male guppies have large, colorful tails while the female's tail is smaller and more plain.
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Tips & Warnings
The female's gravid spot grows in size the closer she is to giving birth.
Guppies are cannibalistic, so if you want to keep the fry, move the female to a rearing tank or birthing box before it gives birth.
