When Can Baby Guppies Go in the Main Tank?

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Guppies are fantastic breeders, which means that, whether you like it or not, you need to learn how to deal with guppy pregnancy. One of the main points of interest here is how to handle the resulting fry.

Allowing the female to give birth into the main tank may result in overcrowding. This means that you need to separate the pregnant female when the labor sets it and have the fry spawn into a different environment.

But when can you add them back to the main tank? And, most importantly, what should you consider before doing so?

Today, we will discuss guppy fry and what you should do before introducing them to the main aquarium.

Factors to Consider Before Mixing Baby Guppies With Adults

While guppy fry often get eaten by adults, there is a problem not everybody is aware of. Guppies are in fact cannibals. This, in fact, is a fish problem more than a guppy one since most fish species will eat their own under the right circumstances.

Here’s what to consider before mixing the fry with the adults:

– Baby Guppy Size

One such circumstance I’ve mentioned previously is the size difference. If your guppy fry are too young and small, the other tank inhabitants will see them as food. This stays true to the ‘big fish eat small fish’ saying that will govern all environments, whether natural or manmade.

The situation is so volatile that even guppy females will eat their own fry upon birth.

To prevent that, I recommend allowing the guppy fry to reach a decent size, allowing them to outgrow their prey status. Adult guppies will no longer attempt to eat them, providing the fry with a safer environment as a result.

How large the fry should be will depend on the type of fish inhabiting the tank.

Generally speaking, the fry should be at least 1 inch in size before introducing them to the main tank.

– Age of Baby Guppies

Age and size are generally correlated when it comes to guppies. The older they are, the bigger the guppy will get within its species’ limitations. How long will it take to reach the ideal size, you might ask?

That depends solely on the environmental conditions, mainly food and water temperature. Guppy fry require a varied diet, preferably with more protein and animal fats than the adults.

I suggest feeding your fry a homemade paste containing multiple ingredients like egg yolk, beef heart, brine shrimp, daphnia, spirulina, veggies, etc. These will provide your guppy fry with key nutrients, boosting their development and keeping them healthy and strong in the long run.

Water temperature is another key asset. Guppy fry should enjoy a temperature of around 80 °F, as this is ideal for young guppies during their growth phase.

– Baby Guppy Health Condition

This is a key factor, showing why you should always separate the pregnant female from the general population before giving birth. Some of your fry may develop a parasitic infection or a disease that could spread to all the other fish.

It can be a tragedy to introduce a sick fish into your main tank, especially when the symptoms aren’t that visible. The 2-3-week period that it takes for your fry to reach their ideal size for the main tank will also function as a quarantine time.

This will allow you to monitor the fry and detect any diseases that might endanger your guppy population. Treating the condition is essential before releasing the fry into the main tank since even minor conditions can advance to more severe levels.

– Hiding Spaces

Even if guppy fry are of the ideal size, they still need a secure environment to protect themselves from the adults and other bigger fish. Make sure your main tank has plenty of hiding places that your guppy fry can use to feel safe and comfortable.

This will also minimize stress, lowering the guppies’ immune system over time.

There are numerous tank decorations, plants, wood, and caves you can use to ornate your aquarium and keep the fry safe.

– Number of Adult Guppies

Having a smaller number of adult guppies will minimize the impact on the fry. Essentially, you will have fewer adults hunting or stressing them throughout the tank.

A small number of adult guppies is also necessary if you plan to add multiple fry into the tank. If you already have an extended adult guppy population, the addition could lead to overcrowding.

How to Add Young Guppies in the Main Tank?

If your guppies are ready to go into the main tank, you must prepare them for a smooth and safe transition. Remember, guppy fry will live in a slightly different environment with different water parameters. For instance, their environmental temperature may be higher than that in the main tank. And that’s not the only parameter that counts.

To transfer the fry safely, you have 2 strategies to care for:

– Feed Adult Guppies First

If you don’t feed your adult guppies before introducing the fry, they might see the newcomers as food, especially thanks to their smaller size. Feeding the adults will minimize their aggression, allowing them to be more welcoming and peaceful, at least for several hours.

This will give the fry enough time to accommodate to their new environment and work their way around the habitat. It won’t take long for the fry to find the most useful hiding spots and learn how to navigate around the tank to avoid the adults.

– Ensure Gradual Acclimation

This process will gradually accommodate the fry to the main tank’s condition, minimizing the shock of changing environments. The steps to undergo include:

  • Gathering all the fry in a plastic containing their own tank’s water
  • Placing the container into the main tank and leaving it there for about 30 minutes – the goal is to equalize the temperatures between the 2 environments.
  • Add a bit of tank water into the plastic bin every several minutes until the container is full
  • Allow the fry to accommodate to the mixed water for another 30 minutes or so
  • Move them into the main tank using a fishnet – throw away the water from the breeding tank; don’t pour it into the main tank along with the fry.

The acclimation process will allow the fry to adapt to their new environment with minimal discomfort.


Guppy fry require slightly different environmental conditions compared to the adults. If you’re unsure about their ability to acclimate properly or don’t want to face the risks, have the female give birth in the main tank.

The fry will survive (most of them, at least) so long as there aren’t enough adults to hunt them down. Adult guppies are also less likely to hunt the fry if they’re already full and happy with their diets.

Otherwise, separate the pregnant female from the main tank, grow the fry until they’re 3-4 weeks old, and gradually acclimate to the main tank. I also suggest monitoring the water parameters in the main tank to make sure they’re as close as possible to those in the breeding tank.

Updated: December 10, 2021
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