How Can You Tell If A Guppy Is Male Or Female?

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One of the major attractions to keeping guppies is the fact they are a live-bearing species of fish. This means the female guppies give birth to live, free-swimming baby fish. Get yourself a pair of guppies and within 3 to 6 months you can have hundreds of baby fish swimming around your aquarium. If you are new to guppies, you may be wondering ’How can you tell which guppies are male and which are female?’

When it comes to guppies, identifying which fish are male and which are female is relatively simple. The male fish tend to be very colorful with long flowing fins. Female guppies are usually a uniform silver to cream color, with a small amount of color in their tails.

Guppies are one of the most widely kept species of fish in the freshwater fishkeeping hobby. Guppies have been kept and selectively bred since the 1960s. Today, there are literally thousands of different color variants available and about a dozen different tail shapes to choose from.

What Are The Differences Between Male And Female Guppies?

I have been keeping guppies for nearly 30 years. Over that time I have probably kept several thousand guppies and I still find myself fascinated by this wonderful fish.

One of the things about guppies that really amazes me is the fact males and females are so different. Some of these differences include;

  • Coloration
  • Body Size
  • Body Shape
  • Reproductive Organs


Male guppies are the ones with all the colors. Over the years guppies have been selectively bred into a kaleidoscope of different colors. I have always been drawn to the yellow and the red strains of guppies. I think over the last 3 decades I have probably kept almost every color strain there is.

The females in contrast tend to be a uniform silver to cream color. Female guppies will often have a little color in their tails, but nowhere near as much as the males.

Body Size

As well as having more color, male guppies are slightly smaller than females. A male guppy will grow to around 1” to 1.5” long whereas a female guppy will easily grow to 2”-2.5”. I once had a female who was closer to 3” long.

Body Shape

Male guppies are slender fish. They are designed to be able to swim quickly. They dart around, showing their brightly colored tails off to the females, before nipping in and trying to mate with them. Female guppies on the other hand tend to be a lot stockier. They are broader across the ‘shoulders’ and much rounder in the stomach.

Reproductive Organs

A final way to tell the difference between male and female guppies is their reproductive organs. Male guppies have a pointed analfin. This modified fin is used to fertilize the female guppies. This modified fin is called a gonopodium.

What Age Can You Sex Guppies?

During the first 3 weeks of their lives, guppy babies are identical.

When guppies reach 4 weeks old, the male guppy babies start to develop the gonopodium. If you are trying to sex the baby guppies at just 4 weeks old, you will need to check the fish at least once a day as they develop quickly.

When I am actively separating my male and female guppy babies, I check them morning and evening.

Does Male To Female Ratio Matter?

Male guppies are obsessed with breeding. They spend their entire day trying to copulate with female guppies. Male guppies are very persistent and that persistence can take its toll on the females. Male guppies can literally harass a female to death. Spreading this attention across several females reduces the stress on the individual females.

I have found that keeping 3 or 4 female guppies to every male is the best male-to-female ratio.

Does Water Temperature Affect Guppy Fry Sex?

The internet is full of stories about how water temperature during pregnancy affects the male-to-female ratio of baby guppies. In my experience, water temperature makes little or no difference to the sex of baby guppies.

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

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