How Long Do Guppy Fry Need To Be Separated?

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One of the first questions I asked myself when I first grew guppy fry was how long they should be separated from their parents and other fish. I knew this was important because guppy fry can be easily eaten. Fortunately, as years passed, I gained some experience in this field.

Guppy fry should be separated for 6 to 8 weeks. That will allow them to grow to a size of one to two inches, in which they can’t fit in their parents’ mouths. But if the aquarium features large and aggressive fish, such as cichlids, it is better to wait at least four months.

As we move forward, I will explain how long you should wait before introducing your guppy fry to other fish. I will consider the tankmates, whether you’re using a breeder box, etc. Then, I’ll discuss what you should do while your guppy fry are separated.

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 Do Guppy Fry Need To Be Separated?

When a guppy falls pregnant, you have to keep it in a breeding box or a separate tank until it gives birth. Once the mother pushes all the guppies out, you can send her back to the main tank. 

The goal is to prevent the female guppy and the other adult fish from eating the babies. But the babies cannot stay in a separate tank forever. Eventually, you have to introduce them to the main aquarium. 

To identify the right time to make this transition, you should take the following into account:

1. The Life Cycle Of A Guppy Fry

The life of a guppy usually consists of four stages, namely:

  • 0 Months – Guppies are at their smallest when they are born. They are ¼ inch long. They also appear deformed. Though, this changes after a few hours. Because guppies are livebearers, the babies start swimming soon after their birth.
  • 2 Months – Guppy babies will grow a lot in the first two months, especially if they have a decent diet and stress-free aquarium conditions. Many will reach ¾ inches by the third month.[1]
  • 4 Months – At this stage, the guppies are sexually mature. Most of them are still ¾ inches, but a few can reach the full 2 inches at this stage. The average size of an adult guppy is two inches.

Once you know the guppy fry growth stages, you can identify the right time to introduce the babies to the aquarium. Your biggest concern is the size. You separate guppy fry because you don’t want the adult fish to eat them.

The temperament isn’t the problem. Even if your adult guppies are peaceful, they will eat the babies because they have confused the creatures for food. You can blame this on their small size.

Therefore, the best way to protect the fry is to make sure they are too big to eat before adding them to the main tank. Based on the lifecycle, you can tell that, at six months, the guppy offspring are too big to be eaten because they have reached adulthood.

Some people are convinced that two weeks is enough for a guppy fry to grow to a size where the adults won’t eat it.[2] But 14 days is not a lot of time. 

Generally, you should aim for 6 to 8 weeks.[3] Give the babies as much time as possible to grow. Don’t be so quick to rush them out of the nursery. The bigger they are, the better their chances of surviving.

2. Breeding Tanks vs. Breeder Boxes

The environment also matters. Breeder boxes are not popular because they are considerably small. Some aquarists have accused breeder boxes of interfering with the growth of their guppy fry because of the stress they induce.

This is why people rush baby fish out of breeder boxes. They are more likely to introduce the fry to the main tank within two or three weeks. On the other hand, people with separate breeding tanks are more likely to take their time. 

If the breeding tank is large enough, some aquarists will wait until the fry are full-blown adults (6 months of age) before adding them to the main aquarium.

They don’t have a reason to rush the babies out of the nursery, especially if the conditions in the breeding tank are just as conducive as those in the main aquarium. 

3. The Physical Appearance Of Your Fry

You don’t have to concern yourself with guppy lifecycles. At the end of the day, the goal is to keep the babies out of the main tank until they are too big for the adults to eat them.

Rather than waiting the prescribed 6 to 8 weeks, some aquarists will base their decision on the appearance of the fry. If the babies look like they are too big to fit in the mouth of an adult guppy, the aquarist will move them to the main tank.

If they still look small, the aquarist will keep them in the nursery. This method is perfectly acceptable if you have experience with fish because you can trust your judgment. 

If you have doubts, you can always measure the babies. This is a delicate process. You must measure the creature from the snout to the tip of the tail. You have to take the fish out, measure it, and return it to the water as quickly as possible.[4]

The babies should be at least an inch in length before you move them to the main tank. You don’t have to measure every guppy fry. Measuring a few fish is enough to give you an idea of what the babies look like at different lengths. 

4. The Tankmates In Your Aquarium

A 1-inch fry can survive in an aquarium with adult guppies, but only because adult guppies have an average size of two inches. But what if the tank has larger fish from other species?

For instance, goldfish are peaceful creatures that can coexist with other fish.[5] However, their size is a problem. Some of them are just four inches. Others can grow to a size of 8-12 inches.[6]

A 4-inch goldfish may attack a 1-inch baby guppy. Oscars are even more problematic, as they can easily reach 15 inches in a large tank. Additionally, they have an aggressive streak. 

Therefore, the sizes and temperaments of the fry’s potential tankmates will influence the timing. If all the adult fish are small and peaceful, you can transfer the fry to the regular aquarium within a week or two.

But larger tankmates should give you pause. Naturally, young guppies can still survive in a tank with aggressive Oscars. The key is to add plenty of plants and decorations to hide the fry.

Even in a conducive environment, roughly 30 percent of baby guppies survive. Therefore, the death of a few fry at the hands of violent tankmates shouldn’t shock you. It is to be expected.

5. Producing More Fry

Keep the sexual maturity of the babies in mind. If you don’t want to produce more fry, moving the babies back to the main tank is simply the first step. Eventually, you have to separate the male fish from their female counterparts.

You don’t have to do this the moment the creatures are born. Just remember that the female guppies are ready to reproduce at 2-3 months.[7] Some people separate the fish the moment they are large enough for you to determine the gender. 

What Should I Do While The Guppy Fry Are Separated?

As I mentioned earlier, only 30 percent of your guppy fry are expected to survive. But there are still things you can do to maximize your chances. Start with adjusting the water chemistry.

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, ammonia, nitrates, and nitrites, I personally use the well-known API Water Test Kit (link to Amazon). While this kit is a bit more expensive than average, it is highly accurate and lasts for roughly eight hundred measures.

If the water conditions are appropriate, you can move forward to the next step, which will be providing your guppy fry with enough room to swim. As I mentioned earlier, breeder boxes can be too stressful for baby guppies.

That is why I suggest installing an aquarium divider. You can then grow the parents and the fry in the same aquarium without worrying that the babies will be eaten. Here is an excellent video that will show you how to do that:

Make sure you feed your guppy fry four to eight meals a day. After two months, you can reduce it to three times a day. If you are not sure what food to use, here is an article where I discussed what baby guppy fry eat

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.


Guppy fry should be separated for approximately 6 to 8 weeks. That will allow them to grow into a size in which they cannot be eaten by most fish, including their parents. 

The best way to keep them separated is by using an aquarium divider. That will allow the guppy fry to grow in the same water they are used to. While they are separated, make sure you feed them nutritious foods at the right frequency.