How Big do Guppies Grow in Size?

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Guppy fish that are offered enough space, the right water parameters and a high-quality diet, will develop into beautiful and healthy adults.

While guppy fish size can be largely dependent on genetic factors, the external factors I mentioned will also contribute to their growth.

Guppy fish kept under the right conditions and with a good genetic background can reach average sizes of 1.5-2 inches. Some guppies can grow even bigger (3-3.5 inches), but they count as a rarity in home aquariums.

If you want your guppy fish to grow and develop in a healthy way, in this quick guide to speeding up guppy growth rate I will walk you through the do’s and don’ts of raising guppies.

Common Reasons Why Guppies Stop Growing

Before I discuss the ways you can accelerate the growth rate of guppies, let’s get an overview of the reasons why guppy fish may stop growing:

1. Aquarium Space

Lack of space can easily prevent guppy fish from growing, especially while the fish are still developing.

Regardless of whether they’re in the fry stage, the juvenile stage of their growth, or the adult stage, guppy fish require enough aquarium space.

The recommended aquarium size for a starter pair of guppy fish is 10 gallons, which is also the same size required for raising guppy fry.

If you can go bigger or if you’re planning on keeping more than 3-5 guppies in your aquarium, a 10-gallon starter aquarium will no longer be enough, and you’ll need to up the size of the tank.

2. Water Parameters

If water parameters in the aquarium are not within the optimal range for guppy fish, your guppies will have problems developing as they should.

Temperatures that are off, lack of oxygen, the accumulation of toxins in the aquarium will all adversely affect the growth rate of your fish.

Therefore, make sure to invest in a heater, a filter system and to perform water changes regularly to keep the water at the required temperature and do away with toxins.

3. Crowded Tank

Having an overstocked aquarium will no-doubt stunt the growth of your fish and cause a series of other health issues because of the lack of oxygen, high toxins levels, and the stress of being in a crowded tank.

If you have a small aquarium and with the rate of guppy breeding, you may easily end up with an overcrowded tank, so make sure to have a spacious tank for the number of fish you’re keeping or rehome some of your fish.

You should also pay attention to male to female ratio (1:3) and control the population in your tank by preventing breeding, i.e. keep only male guppy fish, for example.

4. Genetics

Genetics is also a crucial factor that can prevent your guppies from growing to larger sizes. You can breed guppy fish for various traits including color, patterns, and even size.

But if the genetic material that you’re working with isn’t lending itself to produce larger specimens, your efforts to grow larger guppy fish will not pay off.

5. Food

If you’ve been following my blog, you know that I am an advocate of offering your guppy fish a varied diet above all.

High-quality foods coupled with variety will ensure that your fish get the nutrients, vitamins and proteins they need to grow and build an immune system that can kick diseases to the curb.

Don’t just feed your guppies flake foods, however great they may be in quality, offer them frozen and freeze-dried alternatives and even live foods if their source comes from a controlled environment.

Now that you know what are the factors that prevent the growth of guppy fish, let’s see what you can do to increase the growth rate of guppy fry and guppy juveniles.

Speed Up Growth Rate of Guppies

If you want your guppies to grow faster, you should:

Offer them enough space in the aquarium

Because the lack of space can stunt their growth, make sure that your aquarium is spacious enough for the number of guppies you’re planning on keeping.

If you’re unsure how many gallons are needed, a good rule to follow is the 1 gallon of water per 1 inch of fish.

Undersizing the aquarium is bad, but if you’re keeping fry oversizing can also be an issue, because the fry may not be able to efficiently search for food if the water volume is too high.

Therefore, it’s a good idea to get a bigger size aquarium, just make sure it’s not way too big.

Make sure water conditions are optimal

 Optimal water conditions means having stable water parameters in the range required for guppy fish to thrive.

For this, you will need to invest in additional equipment such as a heater, filter or lighting system. It’s also beneficial to have live plants in the aquarium, which help keep the water clean and it can also provide a source of food and offer shelter for guppy fry.

You’ll also need to perform weekly water changes at 15-20% of the water volume to replenish the water, dilute and remove toxins.

Offer them a varied and high-quality diet

Diet is crucial when guppy fish are still developing. Nutritional deficiencies can lead to deformities and diseases, so make sure to create a feeding schedule and introduce your fish to a variety of foods suitable for them.

Guppy fry should be fed multiple times a day (I like to feed them 5 times a day), while adults can be fed once or twice a day.

Guppy fry require a protein and nutrient-rich diet, which can be offered by live foods such as baby brine shrimp, micro worms, daphnia, vinegar eels, etc.

Keep males and females separated

Because guppy juveniles become ready to breed at around 3 months, female and male guppies should not be kept together.

While they still have growing to do, breeding will consume a lot of energy that should be used for growing instead.

You can also separate guppy fish by size, so that smaller guppies can get better chances of getting access to food.

When do Guppies Reach Their Maximum Size?

Guppies usually stop growing at around 6 months. At this point they’re already adults, they can breed, and are fully developed.

Depending on genetic factors, some guppy fish may continue to grow a bit more (especially males may grow longer tails and fins), but usually they reach their max size at 6 months.

How to Breed Guppies for Size?

Breeding guppies for size is not easy. You need to have some breeding experience under your belt and a lot of patience.

It takes a lot of time and multiple generations of selective breeding to increase the size of guppies as a species.


Guppy fish remain relatively small, especially in home aquaria. With good diet, good keeping conditions, and selectively breeding across multiple generations, you may be able to create larger specimens.

By following the advice I give in this article, you can make sure that your guppy fish will reach their expected average size.

Remember that genetics is only one factor in determining growth rate and size, and other factors like water parameters and diet can play an important role as well.

Updated: August 24, 2022
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