Why Do Guppies Eat Their Fry? And Can You Prevent It?

Guppies are one of the most common fish for home aquariums. They are easy to care for, and quite hardy, so the guppy is a great option.   They are tropical fish, which come in a large range of colors, and is why they are often called rainbow fish. The name million fish comes from another reason because they can give high numbers of young. The issue is, adult guppies are known to eat their young.

For new tank owners, this poses a question until they are aware of the answers.

Why do guppies eat their fry? And can you prevent it? Scientists are not entirely sure why adult guppies eat there fry. While some thing that it is to sort the weak from the strong, this doesn’t appear to be the case. Additionaly, in the wild, a mother will have a chemical released in her brain that makes her not hungry. While supposedly making her ignore her fry, this again sin’t the case in aquariums, and she will still eat her young.

Filial cannibalism, is a common practice among guppies. Often guppies will not show any concern for their fry and use them as a food source immediately after they are born. This though isn’t the only reason they will devour their fry.

Read on and you can learn more about why they eat their young, and what you can do to help prevent this action.

Top Reasons Guppies Eat Their Fry

Guppies do partake in filial cannibalism, yet it should be known, they aren’t the only fish to do so. While there have been countless studies over the years as to why they do this, there has been no concrete evidence which delivers a solid answer.

Here are a few of the top reasons guppies may eat their fry:

  • Stress: Many scientists belive that this fry eating stems from responses to stress. It is a self preservation instinct that kicks in as a response to stress. This can come from many areas such as hunger, temperatures and overcrowding among others. This explanation isn’t justified because when fish are removed from stressful conditions, they still show signs of cannibalism.
  • Sorting the weak: One further thought of filial cannibalism is that adult fish take part in this to sort out the weaker of their young. When they kill off the weaker fry, it increases the chances of the stronger fry to survive. The targeted fry will show they are genetically weaker, or they lack strong survival characteristics.
  • Replenishing energy: Other explanations think that these actions are the mother replenishing fat deposits she lost while giving birth. The problem here is that male guppies also eat their fry, and they don’t take part in the process of childbirth.
  • Lack of food: Moving on from this is the train of thought that both adults eat their fry as a means of supplementing their diet when food sources are scarce. In nature, if there is a distinct lack of food, it makes sense to eat what is in front of you. Once again, this thought doesn’t remain true because if you feed your guppies well, some will leave the fry alone, while some still decide to eat their young.

Even though there is no clear indicator of the reasons, and the most probable causes being self-preservation and the continuation of the species with strong specimens. There is still the issue of guppies eating their fry, no matter what the reasons.

Now, we will look at what you can do to help your new guppy fry survive, and to prevent the parents from carrying out filial cannibalism on their young.

Preventing Guppies from Eating Fry

Although research suggests that cannibalism among guppies is instinctive, there are things you can do to help prevent this from happening with your own guppies. 

Here are some ways you can help filial cannibalism in your aquarium.

Use Breeding Boxes

These are simple contraptions and are made from mesh or clear plastic. You hang these on the side of your tank, and to it, you will add the female guppy that is close to giving birth. Water can flow through these, so the conditions for the female are the same as your main tank, however, the bottoms are slatted or have holes where fry can swim to be safe.

Once the mother gives birth, she can be removed and placed back into the main tank. The fry can stay in the breeding box until they are large enough to be added or moved. This should be two weeks, and any longer, and you can find your fry have stunted growth.

An advantage of this is your new fry will be acclimatized to the water conditions immediately.

Use a Breeding Tank

It is possible to set up a separate tank for the pregnant guppy. When she is about to give birth, you can transfer her from the main tank into the second tank. It is advisable to do so with a large cup and tank water than using a net.

If you spot a rounded abdomen, the guppy is becoming reclusive and there is a dark mark in the shape of a V on her belly, then she may be close.

Once she does give birth, you will have to transfer her back to the main aquarium, or she will likely start eating her fry.

This is a method which takes up more effort and cost. You need additional filters, heaters and lighting. It will again be around two weeks before the fry are large enough to be transferred to your tank, or to another.

Offer Lots of Places to Hide

This can be the easiest way, yet it does involve lots of risk. For many aquarium enthusiasts who are doing this for fun, it can be the better option.

Introducing lots of places to hide for the young fry can in some cases be all it needs for amny of them to survive. It is the most natural way, and if you are happy to let nature take its course, then adding lots of plants, ceramic caves or anything else that delivers small holes and dark spaces for them to hide.

Live plants are the best options, and adding more of these will help to remove toxins from your tank water.

Caring for Fry in Separate Breeding Tanks

To ensure that your baby guppies stay healthy, they require special care in the first couple of weeks.  Here are what you need to deliver them:

Clean Water

Any breeding tank will need a water filter. Fry will have weak immune systems, and are vulnerable to disease. Dirty water can quickly make them ill, and they won’t have the strength to survive.

Even with a filter, there may still be a requirement to change the water by at least a quarter of the water volume every time. 


Fry will require around eight to twelve hours of light per day. If they are left with insufficient lighting, they can grow with deformities. Placement should ideally be on the top of the tank. To be sure you are delivering the right amount of light, you can purchase LED aquarium timers that will turn on and turn off your lights automatically.


Fry will gorw fast and will need feeding several time throughout the day. Guppies are omnivores and can eat diets of meat, flakes and live or frozen foods. Until they are large enough, you may need to crush these in to a powder so they can eaily eat them.


Unless you separate the female guppy from the main tank, you may miss the time your guppy gives birth. There is a fine line, and it is this reason whay many aquarium enthusiasts opt for the live plant option and offering hiding places.

While it is possible to reduce the instances when parents carry out filial cannibalism, even with a breeding box, some of the fry may be adventurous and swim in the wrong area where the mother grabs the opportunity.

No matter what methods you use to try and eliminate this cannibalism, you will need to make sure you care for your guppies in the best possible way. Nature has a funny way of working, but you will have plenty of colorful fish to adorn your aquarium, and they will be able to carry on their family line.