How to Stop Guppies from Breeding

You can stop guppies from breeding by separating them by gender or by keeping only one gender. Separation methods are not always successful as female guppies can store sperm for months on end.

When you want to keep guppies, or million fish, without the population increasing drastically you will need to know what options you have available. To do this, you will also need to know how to identify guppy genders which I will cover below.

How to Stop Guppies from Breeding

Keeping your guppy population from exploding can seem like an uphill battle, but there are a few good methods you can try. These methods might not work immediately due to the ability of female guppies to reserve sperm for months if not years after seeing a male.

However, with enough persistence, you will be able to stop your guppies from breeding. Some possible solutions include:

  • Keep only males or females
  • Separate the guppies by gender

If you don’t want to stop breeding entirely you can also slow the growth of your guppy population in a couple of ways. The two simplest methods include:

  • Keep the fry with their parents
  • Add another fish that will eat the fry

These last two solutions are understandably repellant to some. Whether they are or aren’t, they are efficient ways to keep your guppy population in check.

Guppy Multi Colored Fish in a Tropical Aquarium

Keep Only One Gender of Guppy

The first method is to avoid owning guppies of one gender or the other. This method and the next require you to be able to accurately identify the gender of a guppy. This method is fairly effective once you can do that.

If you only have males there is no chance of any offspring. Unfortunately, the males will likely be aggressive towards each other. If you choose this method be sure to have plenty of hiding spaces in your tank.

If you have only females there will still be a chance for offspring. As mentioned above, female guppies can keep sperm alive for a long time. If any of your female fish have mated with a male before you purchased or separated them they could give birth.

If this happens you can wait it out. Eventually, the guppy will run out of stored sperm. Alternatively, you can purchase virgin guppies. Since guppies reach maturity quickly these virgin fish will be much more expensive and harder to find.

Separate the Guppies by Gender

If you already have a mixed group of guppies or you want to keep both genders you can keep them in separate tanks. This option may not be feasible for all since the two tanks will have to be big enough for your guppies.

Separate tanks also mean you’ll have two tanks to take care of. If you aren’t looking for extra work this option is not for you.

As with the previous method the female guppies can still give birth after being separated so be on the lookout for that.

Keep Fry with Parent Guppies

The problem of too many guppy offspring can be self-solving. Guppies have no parental instincts which means that they will not only neglect their fry but will also confuse them for food.

This method works well if you aren’t concerned with stopping breeding entirely as some offspring might survive. Though some will, the numbers should be greatly reduced.

To facilitate this method, you can remove a few hiding spaces or places that the larger guppies can’t go.

Introduce a Fish to Eat the Fry

This method is similar to the previous one just with a different type of fish. It does come with the added complexity of finding a fish that will eat the young, but not the adults.

Below are a few possible choices:

  • Gourami fish
  • Bristlenose Plecos
  • Betta fish
  • Swordtail fish

Again, you can remove hiding spaces to make it easier for the bigger fish to find the fry.

How to Identify Guppy Genders

Since two of the population control methods require you to know how to identify their genders, let’s go over the most obvious identifying features.

When guppies are very young they won’t have developed their differentiating features. When they are at least one week old they will begin showing differences.

Differences are apparent in three main areas:

  • Size
  • Color
  • Fins


Female guppies will be longer and wider than male guppies. Sometimes the difference can be as much as two times smaller or larger respectively.

You can also distinguish them by the shape of their bellies. Female guppies have rounder bellies than males.


Another way to tell them apart is color. Male guppies will be more colorful than their counterparts. However, some females can be colorful as well.

Males will commonly be blue, orange, black, white, and other colors. Females can be distinguished by a dark spot on their underside called the gravid spot.


On the top of the fish is a dorsal fin. Male guppies will have longer dorsal fins than females. The caudal fin at the end of the fish will also be bigger on a male guppy.

The third fin to look for is the anal fin. This is located beneath the fish. Male anal fins are pointed and narrow. Female anal fins will be wider and shorter.

What to Do with Unwanted Guppy Fry

Even after your best efforts, you may still get some pregnant guppies. If this happens and you don’t want anymore you need to do something about the fry.

The question at this point is what to do with them all.

The first option you have is to give them away or sell them. This is certainly better than letting them get eaten by their parents or other fish. Additionally, if you choose to sell them you can make some money off them.

If you can’t find anyone who wants the guppies you can leave them in with the adult guppies. The adult guppies will likely eat the majority of their young. If you have another fish in the tank they might do the same as well.