How to Control Guppy Population in Your Aquarium?

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Guppies are one of the most well-known and widely distributed tropical aquarium fish for both the beginner and experienced aquarists. It is also known as rainbow fish thanks to its colorful spots, splashes and stripes.

Another well-deserved name for guppy is ‘millionfish’, which makes perfect sense when you think of how easy it is to lose control over the breeding of live-breeder species like guppies.

You may leave your freshly cleaned perfect-looking aquarium in the morning and find it overrun with guppy fry at the end of the day. This thing will most likely happen to you too if you keep guppies in your aquarium.

In this article, I will talk about this common problem with guppy fish and let you in on a few tips on how to control guppy population in your aquarium.

Why Should You Control Guppy Fish Population?

Even if you do have some fishkeeping experience under your belt, chances are you may still run into guppy overbreeding issues only to end up with guppy fry regardless your best attempts to avoid this situation.

What should you do differently next time to make sure this won’t happen again? How can you control guppy breeding? What can you do with unwanted guppy fry?

These are questions I will explore in this article to help you keep your aquarium clean and free of unwanted fry. I will share some ideas on how to manage guppy fry and why you should not let them overbreed.

Being considered as invasive species, guppies breed a lot and if you are an inexperienced or just simply an unlucky aquarist, guppy fry can cause some headache.

Controlling guppy fish population is the best option you have to prevent your aquarium from overrunning with fry.

Let’s see what the reasons why you should take breeding control seriously and what kind of damage can you expect if things get out of hand:

Fry Production and Aquarium Overstocking

You don’t need to be an expert to understand the risks of overstocking. Uncontrolled breeding can lead to the obvious result of overpopulation.

Due to their prolific breeding ability, guppies produce a lot of fry, negatively influencing the cleanliness of water, and being a direct cause of overstocking.

In the case of aquarium overstocking, the visual disadvantage is without doubt an outstanding problem — too many fish in the tank do not necessarily offer the view you have always dreamed of when setting up your aquarium.

Unfortunately, there are other more serious issues triggered by too many fish being stuck in the tank. Fish need space for better quality of life, to swim around, and to be able to reach food easily.

Increased waste production

Whether you are an expert or a beginner aquarium owner, you should know that keeping your aquarium clean is a crucial thing you can’t circumvent.

The frequency of regular tank maintenance can increase and became frustrating if your aquarium is overstocked due to uncontrolled breeding.

The increased waste production will be one of the most dangerous (and annoying!) things you will notice when looking at your aquarium.

An increase in the number of fish will lead to increased waste production. Dealing with this will consume a lot of your time and energy, because you probably won’t be able to keep up with the required water changes.

This can lead to serious issues such as debilitating illnesses or the death of your fish population.

Lowered oxygen levels

If guppies get out of control in your tank and you find your aquarium overstocked with an unwanted number of guppies, lowered oxygen level is another issue you must deal with.

Guppy fish require oxygen to survive. If the oxygen level in the water gets too low, the population of your aquarium will most likely be prone to illnesses and even death.

What to Do with Guppy Fry?

Let’s see what your options are in case it is too late to prevent uncontrolled breeding and you suddenly find your aquarium full of guppy fry:

Give Them Away

Guppy fry can be a nice surprise for your friends or acquaintances that are aquarium lovers or try to raise betta fish, angelfish or carnivore fish.

You can offer the fry as a healthy and nutritious snack. Some friends might take the fry off your hands to raise their own guppy fish.

Sell Them on the Internet

Since everything is for sale and the internet is the perfect marketplace to make great deals, why not try selling your guppy fry for profit?

Take the fry out from your main aquarium, separate them from the parents and grow them out. In a short time, you can sell the guppies on eBay or any other online marketplaces including aquarist community forums.

Let Nature Solve the Problem

If you’re not equipped to move the fry from one tank to another, just leave them with the parents. Here’s what is going to happen: since guppies have no parental instincts, they won’t raise the fry, they will eat them instead, decimating their numbers. So, get comfortable with the idea and let nature solve the problem!

How Can You Control Guppy Fry and Breeding?

Luckily, as I have mentioned at the beginning, there are several options for you to control the breeding of guppy fish.

These instructions don’t require much effort or constant attention, they function well once you carry out the necessary actions.

Let’s see the things you can do to prevent a guppy fry invasion in your tank and how can you control guppy breeding:

Keep Males and Females Separately

If you really want to prevent fry production, your best option is to keep males and females in separate tanks. If you don’t want to see any fry in your aquarium, you must avoid having a mixed-gender tank.

However, you might still get a surprise, because there is a chance that some of the females were already pregnant before you have brought them home. Another thing that can go wrong is the misidentification of genders at the purchase.

What else can you do? If you think you can deal with some fry appearing in your aquarium, keep only one male guppy to 2-3 females in your tank. You still can expect to have some fry, but the situation won’t get out of hand this way.

How can you tell the genders apart? Following this checklist on the differences between female and male guppies will help you:

  • Female guppy fish features a rounded abdomen, while males don’t
  • Male have an elongated anal fin
  • Regarding their size, male guppy fish are smaller compared to females both in depth and length
  • Male guppies are more colorful than females and they have larger tail fins

Reduce Hiding Places

It may sound cruel, but in order to successfully eliminate fry, you should reduce the hiding places in your aquarium.

Fry can easily survive without being taken care of by the parents, as long as they are able to hide until they reach a reasonable size.

Different plants, rocks or other decorative elements offer the perfect hiding place for fry. Don’t forget to check or remove these plants and decorations if needed.

Add a Female Betta Fish with Your Guppies

Another good way to control breeding is to add a female betta fish in your tank. Why? Betta fish are quite aggressive with other species and with other betta fish as well, but females aren’t as aggressive or territorial.

As I have mentioned earlier, fry can be a great food source for betta fish, so they will simply eat the excess fry. The instructions are not complicated at all, just put one female betta fish in your tank and that will easily solve the problem.

It is essential to put only one female with the guppies as multiple females can cause problems. Female betta may attack other betta fish, so in order to avoid any unnecessary hassle, stick to one betta.

As you can see, guppy fry can cause some trouble, but it’s not the end of the world and it no way do they mark the end of your aquarist career.

As livebearers, guppy fish can produce a lot of fry and you will need to figure out the logistics to handle the surplus of fry.


There are a wide range of options to manage guppy overbreeding. To avoid overstocking and uncontrolled breeding, you can keep the females and males separately in different tanks, add a betta female in your aquarium or reduce the plants and decorations fry would find suitable for hiding.

You can even profit from unexpected accidents and the internet will be a great help in this case. Selling the fry for profit on the internet or giving them away for friends is a commonly practiced solution. Some of these options, however, do require you to invest time and money in raising the fry.

Whichever solution suits you best to take care of your “fry situation”, don’t hesitate to act. Timing is essential, the faster you take the necessary steps, the faster you get over the whole situation.

Featured Image: Flickr

Updated: January 17, 2022
Questions & Answers
  1. Al_Martinsen


    Despite I’ve had guppies for years and I like them, I always end up with an invasion of them and I agree with you: controlling their population is crucial to keep them healthy and I think the easiest approach is to add predators. I’m surprised that you recommend a single female betta. Are they specially good at it? I ask because I added 2 german blue rams and they don’t catch all of the babies and always a few of them survive. I have a single coridora in my tank and I’ve seen him chew some fry too (I had no idea they eat them too), and I’m looking for ideas to catch all of the babies. Maybe simply add more coridoras? Maybe a school of fast moving fish (from the tetra family maybe?). Any extra idea is more than welcome 🙂

    1. avatar

      Hey! Bettas are very good at hunting baby guppies. I’ve tested this. I think that it was a mistake that your cory has eaten a guppy fry. They usually not good at catching the fry, however they might chew on a perished fry.
      I think that if one or two fry survives from each batch, it is still good, because you will not need to buy new guppies when the old die.
      A school of 5-6 rosy tetras will certainly do a good job for catching the fry, but I would still stick with a betta fish.

      1. Al_Martinsen

        Thank you very much Fabian! That’s a very interesting fact about the betta females :). I’ll be sure if they are compatible with my blue rams and if so will get one.

        About the cory, I assure you at it tries to catch fry every evening and he even has a technique: Every evening, when the lights from the tank turn off, all of my guppies freak out and swim to a corner where there’s a little bit of light. All of them, including the babies. At that moment, the cory starts swimming up and down close to the front glass, and moving slightly towards that corner full of guppies, to try to corner the babies at the bottom of that corner (babies try sometimes to hide between the gravel and the glass) and I’ve seen him several times doing it and catching fry. Then he spends a lot of time chewing it, even some times the already dead fry gets out and in to his mouth a few times before he eats it. I couldn’t believe my eyes the first time I saw it, but I saw it several times so I’m quite sure it’s happening.

        Thank you very much for your answer 🙂

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