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Will Guppies Overpopulate a Tank?

Guppies are a popular choice for aquarium hobbyists. Often referred to as rainbow fish because of their bright, colorful patterns, these live-bearers are easy to both care for and breed. Right now, you may be curious as to whether (or not) guppies can overpopulate a tank? Well, I have the answer for you below:

Uncontrolled guppy breeding can often lead to an overpopulated tank. Guppies have an innate ability to breed and can produce many fry – up to 50 at a time! This can negatively affect the water quality in the tank as well as the other aquatic inhabitants including both fish and plants.

Now that you know guppies can overpopulate a tank if their breeding habits go unchecked, let’s discuss this topic further and in more detail. I’ll explain how fast guppies can multiply, how many should be kept together, and which fish help keep guppy populations at bay.

So, if you’re ready to learn more, then let’s get started!

How Fast Do Guppies Multiply?

Under optimal conditions, female guppies can give birth every 30 days to a batch of fry numbering anywhere between 20 and 50! Combined with their ability to mature quickly, bear live young, and reproduce at a rapid rate, it’s easy for guppies to overpopulate a tank if uncontrolled.

How Fast Do Fry Guppies Grow?

Guppy fry grow to maturity quite quickly. It takes only about 3 months or so. Therefore, they have the ability to reproduce rapidly if given the proper breeding conditions such as a large tank with hard, warm water, nutritious food, and keeping them in a ratio of 1 male for every 2 females.

What Size Tank Do You Need for Guppies?

As guppies grow to approximately 2 inches in length, the smallest tank you can keep them in is a 5-gallon aquarium – if you have only 3 of them, that is. Given how quickly guppies reproduce and the likelihood of anywhere from 20 to each breeding cycle, a bigger tank (up to 20-gallons) is preferred.

Do Guppies Need a Big Tank?

When it comes to guppies in an aquarium, bigger is better regarding tank size. A trio can survive in a 5-gallon tank however, a 20-gallon tank is recommended. For breeding purposes, you must have at least a 10-gallon aquarium though you’ll likely need to upgrade to a larger version once reproduction occurs.

How Many Guppies Should be Kept Together?

On average, you can keep 1 guppy fish per every 2 gallons of water. If you choose to keep both males and females, then you should keep them in a ratio of 1:2 in which case, a bigger tank (such as a 10- or 20-gallon version) is required. And since they’re a schooling fish, you’ll wan to keep them in groups.

Why Should You Control Guppy Breeding?

Controlling guppy fish breeding is the way to avoid overstocking your tank. Overstocking has a direct effect on the health of both the fish and the plants in the aquarium. Too many aquatic creatures in a confined water environment will negatively influence the water conditions and cleanliness of the tank.

Increased waste production is one of the biggest problems with an overpopulated tank. Not only is it time consuming to do the frequent water changes that are required but the increased amounts of ammonia and nitrite are highly toxic to fish and can cause illness or even death.

Decreased oxygen is yet another issue with an overpopulated aquarium. Fish need oxygen to survive and if there are too many in a tank, then the oxygen levels will drop too low to sustain aquatic life. As a result, your fish will get sick or likely die.

As well, too many fish make it difficult to see, altering the visual appeal of the tank and thus affecting your viewing pleasure. This will also impact the health of the fish. They need space to swim about freely. They also need to be able to see and reach food, which can be difficult in an overpopulated tank.

What are the Ways to Control Guppy Breeding?

There are a variety of ways to control guppy breeding. The best option is to keep the males and females apart in separate tanks. Having a gender-mixed aquarium increased the likelihood of breeding. Or, if you want just a few fry, then have only 1 male and 2 females to keep your fish population down.

To tell the difference between male and female guppies is easy. Females have a rounded abdomen whereas males don’t. Males have an elongated anal fin and are usually smaller than females. Males are also more colourful and have larger tail fins than their female counterparts.

Reducing the number of hiding places in a tank will also control breeding habits. Guppies breed when they feel comfortable and safe. Hiding places like plants, rocks, and other aquarium decorations help provide this sense of comfort.

Keeping the aquarium slightly cooler than normal will also help control guppy populations. The optimal temperature for breeding is around 80 degrees Fahrenheit (27 degrees Celsius). By reducing the heat to 72 degrees Fahrenheit (22 degrees Celsius), you lessen the chances for breeding to occur.

Limiting the amount and type of food will also help keep guppy numbers down in an aquarium. Since guppies are omnivores, they prefer to eat both plant and animal matter. By giving them fish flakes as opposed to brine shrimp, they’re less likely to breed and if they do, their fry won’t grow as big or as fast.

Can You Have a Tank of Just Male Guppies?

Keeping only male guppies in a tank is a great way to control population in a community tank. Males are preferred over females as they have brighter, more vibrant colour patterns and tend to be more active as well. With only males in an aquarium, there is less stress and harassment among fish.

What to Do with Extra Guppies?

If you choose to breed guppies and end up with far more than you want, you can do one of 5 things:

  • Leave them with their parents – it’s a sad truth but, guppies will eat their own young so if you want reduce their numbers quickly, don’t remove them from the communal tank at birth.
  • Give them away – you can gift your friends or family members on their birthdays or at Christmas with baby fish as a means of reducing your tank population.
  • Sell them – you can sell fry to your local pet shop or place an advertisement online with your community website seeking a good home for baby fish.

Best Fish to Keep Guppy Populations Down?

For guppy population control, you need to keep a few gourami fish in your tank. Gouramis eat the fry of the guppies but won’t bother the adults. They are bottom feeders and stick close to the substrate whereas adult guppies like to swim freely about in the middle or near the surface of the tank.

Some species of cichlids will also help keep guppy numbers at bay. African cichlids, for example, are more aggressive than their South American cousins and will often feed on other, smaller fish in a community tank. Be careful, as they have the potential to decimate your entire fish population!

Adding a female betta fish to your guppy tank will also keep the population down. Bettas can be quite aggressive with others of their own species as well as smaller fish in a community tank. Females aren’t as aggressive as the males and will help keep guppy numbers down but not obliterate it completely!


To conclude, an overpopulated tank is often the result of uncontrolled guppy breeding. Guppies have a profound ability to reproduce and can spawn upwards of 50 fry in a single breeding cycle! This can negatively affect the water quality as well as the other living organisms (both fish and plants) in the tank.

Hopefully, this article has been of help to you. Thanks for reading and happy fish keeping!

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