How to Identify Male vs. Female Guppies

How to Identify Male vs Female Guppies

If you are raising guppies, you must know how to identify the males from the females because if not, then you will soon have a tank that is overcrowded with baby guppies.

It is not that difficult to tell one gender from the other.  Knowing the difference will help you to control the guppy population.   If you want to prevent pregnancy you will have to separate the males from the females and keep them in different aquariums.

What Happens if Males and Females are in the Same Aquarium

Putting them in the same aquarium will equal mating and reproduction and soon there will be more baby guppies than you can count.  The equality of male to female is important. 

For example, if you have six males and one female in the tank, all of them will chase after her and then impregnate her one after the other.  And if the situation was reversed with one male and six female, he would impregnate each female. In either situation, there would be a lot of babies.

The cycle would continue as long as they are together.  The female also has the innate ability to store unused sperm for later would always make her pregnant.  This would even happen after she just had given birth to a large number of babies.  

How to Identify Male vs. Female Guppy

You can start to tell the difference between the male and female when they are a week old.  At this age, they are still not an adult, which will happen when they are a month old.  Once they become adults, mating and pregnancy will happen.

male and female guppies

1. Body Shape

  • Male:  They look longer and have slender bodies.  The males will grow up to one and a half inches.
  • Female:  They look bigger, curvier, or rounder in size and some females could even be double the size of the male.  When she gets pregnant, her body will grow in size.  The females will grow up to two inches.

To get a better look at the guppies while they are swimming around the aquarium you will need a magnifying glass to get an accurate observation.  

2. The Gravid Spot

This is the spot that is found near the tail, is quite dark and is an indication that the guppy is a female.  A male will never have this spot.  When she becomes pregnant, this will grow darker in color and larger in size.  This is formed because of the eyes of the developing baby fish pressing against her belly.  When the babies are released, then the spot will start to get lighter. 

When she gets pregnant again, it will darken.  If you want to get a clearer view of it,  put the female in a clear glass and use some type of bright light to see it.  You can always use a magnifying glass to give you a better view of it to get accurate results if she is pregnant or not.

3. Coloring

Of the two genders, the male is more colorful and will be the ones to have more vibrant, sensational colors.  Their whole body will be covered in bright colors; blue, violet, black, orange, spots, or white stripes. 

The males will use their attractive colors to get the attention of the female to start the mating process.  In general, the guppies will provide a wonderful display of color in your aquarium.  Although it is rare to find them, some females are just as colorful as the males.  Because of this possibility of it being a rare female with bright colors, you will need to go on more than color when determining the gender.

guppy in aquarium

4. Caudal Fin

The caudal fin is known as their tail fin and the males will have long, wide, and colorful caudal fins while the females are not as wide and are shorter.

5. Dorsal Fin

This is the fin that is found on the top of the guppy near their head.  The males will have the bigger dorsal fin that flows in the water when they are swimming.  The female’s dorsal fin is smaller and shorter.

6. Anal Fin

This fin lies just before the tail fin, or caudal fin, and is a bit smaller.  The males are long, narrow, and pointed.  With the female, it is small in size, located below the gravid spot, and is triangular in shape.  The male’s anal fin is what they use to impregnate the female once it develops and protrudes.

Determining the Fry Sex

It has been said that the pH of the water will determine the sex of the baby guppy.  All you need to do is adjust the pH of the water to make it a male or female.  It is said that to get males you will need to raise the pH level and to get females, you will need to lower the pH level.  

Controlling Your Guppy Population

If you want to have a small family of guppies you should have just one male and two females but if you want to have a lot of guppies, you will need two males and four female guppies.  Either of these would be a good ratio of male to female guppies.  You do not want to have an overcrowded aquarium as this is not good for the fish.

The reason that you need to have this type of male to female ratio is that the male will chase the females all the time trying to impregnate them.  The male guppies like to harass the females so that is why you need to have more females than males, specifically one male and two females.  Most of the time the females will reject the males because they are ‘choosy’ 


  • They fry guppies will start to get their normal colors starting at one week until they are six weeks.
  • The guppy will always be the number one choice if you want to have a beautiful aquarium.  
  • The lifespan of the male guppy is shorter when they are placed in a tank with females than when they are with other male guppies.  The desire to always mate shortens their lifespan.
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