How Long Does It Take For Guppy Fry To Grow?

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Having guppy fry for the first time is pretty exciting. I remember the feeling I had a few years back. But those little creatures raise a lot of questions when they are born. For example, almost everyone wonders how long it takes until they grow and reach full size.

It takes four to six months for guppy fry to grow and reach full size. At the age of two months, guppy fry reach sexual maturity, and they can stop being separated from their parents and other fish. Guppy fry may grow faster when appropriately fed and provided with the right temperature.

As we move forward, I will briefly go through the growth stages of guppy fry and explain what they achieve in each one. Then, I will share some excellent tips that I collected over the years. These will ensure your guppy fry will grow healthy and at the right pace.

Still curious? Feel free to check my complete guide on guppy fry. There, I discussed how to care for guppy fry, what they eat, how often to feed them, their growth stages, and much more.

How Long Does It Take For Guppy Fry To Grow?

Guppies breed quickly, and their offspring are pretty hardy. Even without the proper experience, a beginner can save up to four out of every ten guppy fry

If you consult an expert, they may recommend breeding methods that can significantly increase the baby guppies’ survival rate. Under ideal conditions, you will observe the following changes in the fry:

0 Months – Guppies are tiny at birth, just 0.25 inches in size. However, despite their size, the fry are not helpless. Unlike eggs, the fry are living, breathing creatures. They can swim away from danger. This allows them to survive in tanks with predators. 

1 Month – It only takes a month for the differences between the males and females to emerge. The female babies are larger than their male counterparts. Additionally, their tails are more prominent.[1] 

2 Months – The babies will become sexually mature within two months. Because they are so colorful by this stage, you will notice that the colors are more vibrant in the male offspring. This is a significant difference between the sexes. Male guppies have brighter colors that attract more attention.[2]

4 Months – Most guppies are ¾ inches long at this age. Only a few will reach 2 inches after four months, which is the average size of an adult guppy fish. Either way, guppies can entirely breed at this age.

6 Months – Guppies reach adulthood at the age of 6 months. Adult guppies have an average size of 2 inches. At six months, the offspring can coexist peacefully with their parents in the same tank because they are too big for the parents to eat.

What Is The Fastest Way To Raise Guppy Fry?

It should be noted that external factors can affect a guppy’s growth rate. In fact, commercial aquarists will take the following steps to increase the rate at which their guppy fry grow:

1. Maintain A Temperature Of 80 Degrees F

The temperature is vital to a baby guppy’s growth. High temperatures increase metabolism. They also encourage faster growth. For instance, guppies kept in 80-degree F tanks will grow quicker than guppies dealing with temperatures in the mid-70s.[3]

Colder water will make the guppy fry less active. It can also lower their appetite, discouraging the creatures from consuming the nutritious meals they require to mature quickly.

2. Remove Toxins Like Ammonia And Chloramine

Hygiene is just as important as temperature. Dirty water can impede a guppy fry’s growth. This is because dirty water exposes fish to diseases.

Toxins like ammonia, nitrites, and chlorine will lower the guppy’s immune system, making the babies vulnerable to debilitating diseases.

Don’t forget: baby guppies are more sensitive than adult fish. They cannot withstand the destructive consequences of a dirty tank, and most of them will die. 

If the babies survive, slow growth is the least of your concerns. The poor conditions can stunt the development of the fish. But the fry are also likely to develop long-lasting illnesses and deformities.

Regular maintenance is vital. You should change a third of the water every week. Though, water changes cannot keep the tank clean, not on their own. 

You must remove pollutants like dead fish and rotting leftovers from the water before they destroy the tank’s chemical balance. 

You should also invest in an efficient filter whose strength matches the size of the aquarium. The filter’s GPH (Gallons Per Hour) should be at least four times the tank volume.[4] 

As a rule of thumb, these are the best water parameters for guppy fry: 

  • Temperature: 78-80 degrees F 
  • pH: 6.8-7.6 
  • Hardness: 8-12 dGH 
  • Ammonia: 0 ppm 
  • Nitrites: 0 ppm 
  • Nitrates: <20 ppm

To measure the pH, nitrates, nitrites, and ammonia levels, I personally use the API Water Test Kit (link to Amazon). This bundle is highly accurate and lasts for eight hundred measures, making it pretty cost-effective.

Typically, if the water parameters are out of range, it is best to perform more frequent water changes. But with guppy fry, you should take a more gentle approach, such as using water conditioners. Drastic changes might do more harm than good.

To stabilize the environment and prevent further fluctuations in water chemistry, I suggest getting the Seachem Prime Conditioner (link to Amazon). It also takes care of chloramines, which are abundant in tap water.

3. Provide Half A Gallon For Each Fry

How much room do your baby guppies need? Well, the answer to this question is more complex than you realize. Naturally, you don’t want to crowd your fry. 

You should also consider that a guppy fry will not grow to fit the size of the aquarium. This myth has persisted for a long time. 

Some people think that the tank size determines the fish size. In other words, a fish in a large tank will grow to its proper size while a fish in a small tank will remain small. 

But fish cannot control their size. A fish in a small tank will grow to its proper size. But then, it is more likely to die because of the crowded conditions.

Crowded conditions induce stress, and stress can stunt the growth of some babies. But is a large tank the solution? The average aquarist will tell you to get the largest aquarium you can find, but that is not sound advice.

Too much space is terrible for fry. They can quickly starve to death because they can’t find food. And even if they find it, they will expend large amounts of energy to get to the food. 

This causes stress, which can either reduce the guppy’s growth rate or stunt their growth altogether. You need 0.5 gallons per fry for newborns and one gallon per fry for babies one month or older.[5]

4. Feed The Newborns Four Times A Day

I highly recommend feeding guppy fry at least four times a day. Four times may sound like a lot, but some babies eat as many as ten times a day. They have voracious appetites. You should satisfy their cravings without overfeeding them.

This is why some beginners use automatic feeders. Automatic feeders cannot forget to feed your fish. You can also trust them to add food in the right quantities. They eliminate overfeeding and underfeeding.

As your guppy fry grow, you can feed them less and less. After two months, they should eat three times a day. After five months, you can cut down their meals to twice a day.

I also suggest paying attention to the quality of the food. Give them a blend of plant and animal matter. Live foods at the best option, including micro worms and bloodworms. 

But if you can only afford to feed them flakes, aim for the highest quality flakes. Flakes have meaty and vegetable versions. Get both options. 

Without a balanced diet, you will observe slower growth rates in your breeding tank. For more information on this topic, please check this article, where I discussed what guppy fry eat. I also included instructions and some helpful videos.

5. Create A Natural Day And Night Cycle

Guppy fry need equal amounts of daylight and darkness. Sunlight makes the babies active, and active fish are less likely to contract dangerous diseases.[6]

Try to create a consistent lighting routine, mainly if your aquarium relies on artificial lighting. Fish require sleep, and just like humans, guppies are more likely to rest in the dark.

Unlike humans, they don’t have eyelids. Therefore, the creatures are less likely to sleep when the lights are on. Without these consistent rest periods, the babies will contend with stress, impairing a young guppy’s growth.

This is why some aquarists have chosen to eliminate artificial lighting. They want their fish to rely on ambient lighting, waking when the sun rises, and sleeping when the sun goes down.  

Make sure the ambient light in the room is bright enough before you remove the artificial lighting. That is crucial because you can’t leave the tank next to the window in an effort to expose the fish to ample daylight.

Direct sun will cause the temperature in the water to spike. If the room is too dark, add artificial lights. Keep the aquarium away from the window.

If you found this article helpful, these may also interest you:

Pro tip: If your guppies breed frequently, you’ll need to know a little more about that process. Feel free to check my complete guide on pregnant guppies.


It usually takes about six months until guppy fry are fully grown. But that doesn’t mean they should be kept separated that long. If your aquarium has a sufficient amount of hiding places, they may not need to be separated at all.

If you choose to grow them separately, you can put them back in the original tank after six to eight weeks. In order to ensure the fry grow at the proper rate, it is crucial to feed them four times a day with a nutritious diet.