How to Control Guppy Population in Your Aquarium

Guppies are not just called ‘the millionfish’ as a nickname for nothing. Their reputation to reproduce faster and more than you can imagine precedes them.

There are a few things you can do to control the population of your guppies, such as keeping the males and females in different tanks, Introducing a predator fish, removing plants from your aquirium. I will go in to more detail below

Guppy overpopulation in an aquarium (whether small or large) is commonplace, and most aquarists have experienced it at some point, meeting their recently cleaned aquarium stacked with guppy fry. There are some demerits to having your aquarium overpopulated with guppies and guppy fry:

  • Increased toxins and waste. Overpopulation in a guppy tank will definitely lead to an increase in waste production. No one wants to look at a waste-infested aquarium twice. Of course, you’d have to spend quality time to perform frequent maintenance.
  • Lowered levels of oxygen. Guppies, like all fishes, need oxygen to breathe and survive. But when the tank is overpopulated, there’s bound to be limited oxygen for all of them, leading to illness and/or death.

There are several measures you can utilize to reduce the uncontrolled guppy population in your aquarium:

Separate The Male and Female Guppies

An increase in guppy population is a result of the mating between male and female guppies in the tank.

Even if there’s only a single female guppy inside a tank full of males, it is bound to be pregnant and will release more fry—some of which will be females, and will be impregnated. Uncontrolled, your tank will turn into a vicious cycle of overpopulated guppies.

A way to reduce this menace is to remove the female guppies and keep them in separate tanks. One problem aquarists face at this point is identifying which is which. Professional aquarists can spot female guppies and separate them.

If you have no idea on how to spot them, follow these simple steps below:

  • Female guppy fish tend to be bigger in size compared to their male counterparts.
  • Female guppies possess a rounded abdomen, whereas the males do not have them.
  • Male guppies feature larger tail fins than the females.
  • Males guppies are also more colorful than the female guppy fish.

It is important to note that guppy fry develops their gender during after 4 weeks and can mate after 6 weeks. Hence, it is recommended to separate the females after 4 weeks to avoid mating and breeding.

Introduce a predator fish.

Yes, it seems a little extreme, but introducing a predator fish into an overcrowded tank full of guppies will reduce its population.

Predator fishes will significantly reduce the mating process and the population of guppy fish in your tank. Before including the predator fish, remove the live plants first as it would leave the guppy fry exposed to be eaten.

Some of these predator fishes to introduce include:

  • Tiger barbs
  • Zebrafish
  • Angelfish
  • Paradise fish
  • Siamese fighting fish
  • Large catfish
  • Gourami
  • Bluegill sunfish.

These fishes are bound to lower the rate of guppies in your tank. You can remove the predator fishes when satisfied with the results.

Sell or gift them to someone.

Another way to effectively control the population of guppy fish in your aquarium is to sell them out to fish owners or hobbyists. Guppies look very attractive in an aquarium, hence there are people who may be in search of them to buy. You can advertise on your social media handle and strike a deal with someone willing to buy.

You can also opt to trade them for other species, live plants, or flake foods.

If you don’t want to sell or trade, you can gift them to a friend or family member who is fond of beautiful fishes. Guppies, to the right person, are a wonderful present.

If you don’t fancy introducing a predator fish, this option is doable.

Remove all hiding places.

Another way to control overpopulation is to remove every hiding place inside the tank. This may include large rocks, decorative structures, and live plants.

Guppy fry can survive without parental care as long as they can hide till they get to a reasonable size. Removing these hiding places will leave them exposed to die.

Get an overflow tank

Introducing an overflow tank only provides a temporary solution to the overpopulation problem.

While an overflow tank will reduce the population of guppy fish in the main tank, it will get overpopulated in no time if a lasting measure is not deployed. Which means you’re going to deal with two overpopulated guppy tanks.


This should only be done on extreme occasion, as a last alternative, or when every other measure doesn’t work.

In this case, you select the best guppy fish and put the others to sleep, so to speak.


Guppy population, if unchecked, can be a menace in the long run. If you’re experiencing this sort of thing, you’re in luck. You can try out any of the control measures listed above.

Whatever you choose to act on, it is important to do it immediately as it would save you a lot of stress to deal with later.