Why do Guppies Eat Their Fry?

Guppy cannibalism is nothing new to fish keepers. If you’re a beginner, I recommend keeping adults and fry separated. Being in the same aquarium will encourage acts of cannibalism. These tiny nuggets are supremely tasty, even to those of their own kind. But what is it exactly that leads to cannibalism on fry?

This phenomenon is called filial cannibalism, and it’s quite common to many animal species, not only guppies. Fortunately, there are a few things you could do to prevent adult guppies from eating their fry.

What’s The Cause for Filial Cannibalism?

Most fish species will have some paternal and maternal instincts, meaning they take care of their babies once born. Not guppies, though. Guppies are known to abandon their fry from the very beginning, exhibiting zero parental care. In fact, guppy adults may not even recognize fry for what they are. Instead, they’ll mistake them for food.

Researchers have argued that this phenomenon of filial cannibalism is a spill-over response resulting from stress factors. These factors would enhance the self-preservation instincts of guppies. They’ll eat anything that moves without much prejudice, in other words.

But even when not stressed, guppies will do the same. And other fish species tend to do the same, even when not under stressful situations. But there may be another explanation for this cannibalism – survival of the fittest and artificial selection. Adults want to weed out weak fry, and they will eat those that aren’t skillful enough to survive.

Some of the reasons why guppy fry may be weak include weak genetics or insufficient survival traits. If they can’t hide from their parents trying to hunt them down, they’ll be similarly incapable of hiding from other predators.

So, in a way, guppy adults push forward the survivability of the species by weeding out the weak and inept. It’s a cruel society, indeed, but it works. One more tidbit of information says that female guppies recover their fat storage by eating their own fry. Males don’t replenish anything, though, and they still eat their fry.

Though, regardless of the cause, filial cannibalism is not conducive to a healthy aquarium. Fortunately, there are some things you can do to deal with this:

– Put The Fry in a Breeding Box

You have the main aquarium and then you have the breeding box, a plastic container attached to the aquarium. In the box, you’ll place the pregnant females that are about to give birth to fry. This separation will prevent any event of cannibalism since the guppy adults can’t reach the fry.

Remove the pregnant females once they give birth, though. They, too, have cannibalistic tendencies. But to install a breeding box, the aquarium should be big enough. In this case, size does matter.

A big advantage of the breeding box, aside from the obvious, is that you don’t need to control its water parameters. Both temperature and water quality will be the same as those in the main aquarium.

However, try not to keep the fry inside the breeding box for longer than two weeks. From personal experience, I can say for certainty that their growth will be stunted if they’re kept for too long in the breeding box. After two weeks, most fry should be developed enough to evade their hungry, cannibalistic parents, uncles, and aunts.

– Use Another Aquarium

When your females are about to give birth, isolate them in a different aquarium. In theory, this works the same as with the breeding box, with one key difference – the fry can live as long as they want in the new aquarium. It may be more expensive to set up a new tank, but it’s completely worth it!

To spot a pregnant guppy female, look for the reclusive behavior, V-shaped abdomen, and round belly. Fish it out of the tank and place it in another tank! You’ll need a whole set of filters, heaters, and lights for this new tank, as well.

If you’re in it for the money made from selling guppies, then this investment will be worthwhile. If you’re a passionate nuthouse with a panache for guppies, then it may also be worth it to acquire a new tank.

Before you move the females to a new aquarium, however, ensure that the conditions of the new tank are identical to those of the old one (pH, temperature, hardness, and more). Similar to the breeding box, once the females give birth, remove them from the tank.

– Bring Many Plants to the Aquarium

Live plants – hiding spots for guppy fry. If you want to ensure their continued survivability, the fry will need many hiding spots. And the best way to provide them is through live plants. Plants not only help guppy fry lay low and hide but also clean away the toxins from the aquarium and provide nutrients.

Sadly, this method is not foolproof. It still depends on every individual guppy fry whether it reaches the safety of its hiding spot or if it gets eaten. If you want to sell guppies professionally, then I wouldn’t recommend using this method as a primary method of preventing cannibalism.

The other two are much more effective at achieving the end goal. This is more of a casual and improvised method of dealing with all that fry that you have on your hands. Don’t know what to do with it? Just provide them with hiding spots so they can get to live, at least.

You don’t need to watch over them individually if you use this method. Though, as I said, you may not find the method to be effective. But if you don’t care about the results, then it’s a good a method as any other. When the fry grow and adults can’t eat them anymore, your job is done and you can pat yourself on the back.


Personally, I prefer setting up a separate aquarium, isolating the pregnant females there, and letting them give birth to the fry. Then, I remove the females from the aquarium and put them back into the old tank.

To keep the fry happy and healthy, I feed them about 5 times per day with live food (vinegar eels, brine shrimp, and daphnia), beef heart paste, and flakes. As for the exact cause of cannibalism, I don’t know, and one can only make assumptions. You’ll learn to get used to this, though.

For any other questions, you can leave them down below and I’ll reply within a few minutes!

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

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