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Why Do Guppies Eat Their Own Babies?

Why Do Guppies Eat Their Own Babies?

Guppies often get touted as the best pet fish you can keep. They are beautiful, low-maintenance, and most importantly, easy to breed.

However, things can get quite murky at the breeding stage, if you’re not too careful since adult guppies can feast on their own fry.

Mind you, this widespread phenomenon, known as filial cannibalism, isn’t limited to guppies alone as many other fish species and animal species have shown this trait. So why do guppies exhibit this kind of behaviour? Read on to find out.

Reasons Why Guppies Eat their Own Fry

Filial cannibalism in guppies is something that has puzzled scientists for many years. Various researches have come up with dissimilar reasons on why this species of fish eat their babies.

Some scientists have concluded that cannibalism is a spill-over response caused by various stress factors. This occurs so that the fish can enhance their self-preservation instinct.

Nonetheless, this explanation isn’t satisfactory because even fish that aren’t kept in stressful conditions cannibalize their young. A more realistic argument is that filial cannibalism occurs when parent guppies weed out their genetically weak offspring to increase the survivability of their species.

The fry that get targeted by the parent guppy are either genetically weak offspring or those lacking the necessary survival characteristics.

In other words, by weeding out offspring that will take a lot of time to mature, the parent guppy can conserve their energy for subsequent, faster-developing fry. Another explanation is that female guppies eat their own babies as a way of replenishing their fat storage.

Nonetheless, this argument doesn’t explain why male guppies eat the young ones too. So some scientists have concluded that guppies and other species may be practising filial cannibalism as a food or energy source when other sources are scarce.

But when they supplement their diet, some stop eating their offspring while others don’t. This confirms that filial cannibalism is not all about getting easy meals. Clearly, there isn’t a consensus to why guppies eat their own babies. But many scientists believe the most probable cause is both for the perpetuation of vitalized offspring and self-preservation.

If you want to learn how to care for guppies, please read my linked guide, where I explain everything about feeding, breeding and and raising guppies.

How to Stop your Guppies from Eating Their Fry?

There are various methods of preventing filial cannibalism in your tank. All of them feature one tactic- separating guppy babies from guppy adults. They include:

Use a Breeding Box

A breeding box is a mesh or plastic container that gets installed in your main aquarium to separate the pregnant guppy from the other adults in the tank. Because of its design, water flows out and in of the breeding box, but other fish can’t get in.

So, how do you use a breeding box to save the baby guppies? Here’s a step by step illustration:

Place Pregnant Guppy in the Box

Guppies have an average gestation period of about 22 to 26 days. As such, it’s crucial to continuously watch your female guppies after mating occurs. Mating happens quite fast, which is why many breeders miss to see it. Luckily, there are several clear pregnancy signs that ought to alert you:

  • The mother’s colour appears faded
  • Her belly has assumed a square shape or seems bulged
  • Shes prefers to rest near the heater or hide behind decorations/ plants
  • There’s a dark gravid spot near the guppy’s butt

A few days before the pregnant mother gives birth, place it in the breeder box using a net. Take note that undertaking the transfer make your guppy experience severe stress, which might lead to the absorption of fry. The less time the guppy spends in the breeder box, the less stressed it will be.

Just before labour, the female guppy will appear to be shivering or swimming in place. During labour, the mother will seem to be swimming backwards or pacing about. Labour in guppies can take up to six hours.

The mother usually gives birth to 20-50 fry, one at a time. If she starts swimming calmly, the birth process is over. Newborn guppies are slightly black or coloured grey and measure about 7 to 10 millimetres. Yes, they are extremely small.

Remove the Mother Guppy Immediately After Giving Birth

You ought to remove the mother right after she gives birth as she will feast on the fry. So use a net and scoop the mother guppy from the breeder box. You can then place her back in the main tank.

Allow Baby Guppies into the Main Tank

It’s safe to introduce baby guppies to the main tank when they are about 6 to 8 weeks old. At this age, they will have grown big enough to not fit in the mouth of adult fishes.

The breeding box method is an ideal choice for those who lack a separate aquarium for fry. The best part is that you don’t have to worry about water parameters since the box gets set up within the main tank. Even so, ensure to release growing fry at the right time. They shouldn’t stay in for more than two weeks as their growth will get stunted.

Isolate the Pregnant Guppy

This method involves setting up a separate aquarium tank, complete with all the necessary environmental requirements. Days before the female guppy gives birth, move it into the separate aquarium. You should then extract her after she gives birth, leaving only the fry inside the tank.

It’s important to realize that this method is more expensive than using a breeder’s box because of all the parameters required. Even so, it’s a foolproof way to ensure your fry grow to become healthy, strong adults. Some of the tank conditions needed include:

A Constant Tank Temperature

Baby guppies require a constant temperature of around 76 to 80 °F (24 to 27 °C) to stay comfortable and hungry enough to food required for healthy growth. With that said, you may require a heater to keep the temperature at an optimum degree. Ensure to choose a heater that can handle your tank size.

Take note that cold water will make your fish sluggish, while hot water will harm them. To ensure that your tank’s water temperature is ideal, stick a thermometer to its side.

Clean Water

It’s crucial to install a filter to keep your tank’s water clean throughout. As you may know, baby guppies lack a strong immune system, meaning they are extremely vulnerable to diseases. If the water isn’t clean, it won’t take long for the fry to get infected and die.

In as much as a filter will help you to get rid of any debris and leftovers, you’ll still need to change the water frequently. If you can’t completely change the water, try to replace at least a ¼ of the tank size. You may also need to clean the tank every week to get rid of stubborn baby guppies.

Light for Growth

The fry tank should receive at least 8 to 12 hours of light every day. Baby guppies that grow in dim light tend to develop deformities. Therefore, you’ll need to install a tank light, preferably at the top of your tank. Simply turn on the light in the morning and then turn it off after 14 hours, which should be evening.

Special Diet

It’s worth mentioning that for the fry in the separate tank to grow wholly and quickly, you need to feed them right. Their diet ought to be a mix of beef heart paste, fry flakes, and live foods like daphnia, vinegar eels, shrimp, and brine.

Create Lots of Hiding Places

And last but not least, is the easiest, yet the riskiest method of all. You simply need to install things like live plants, driftwood, coconut cave, ceramic cave, etc. Having such components ensures that your fry have enough cover and hiding spots so that they can successfully elude the adult fish.

Plants are particularly advantageous because they not only provide excellent hiding places but they also help to control your tank’s toxins. Not to mention that they can be a food source for fry.

However, this method isn’t infallible because not all baby guppies will be able to hide in time to not get eaten. Remember, one of the biggest threat to newly born fry is their own mother. Thus, you shouldn’t use this method if you’re looking to breed guppies professionally.

Final Thoughts

There isn’t a given answer to why guppies feast on their young ones. This is something every guppy breeder should accept and prepare for before setting up an aquarium. Otherwise one might suffer heavy losses in terms of the number of fry that get eaten after every mating season.

Of all the methods of saving guppy fry, many avid fish keepers prefer separating the pregnant guppy entirely by placing it in its own tank. Albeit expensive, this method guarantees the best results when it comes to breeding fish. For the best results, create a feeding schedule that involves feeding the young ones five times every day.

Written by Fabian

Hey, I'm Fabian, chief editor at Aquarium Nexus. I really enjoy the aquarium hobby and love sharing my experience with others. If you have any questions feel free to contact me or leave a comment below.

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