Will Koi Fish Eat Other Fish? Do Koi Eat Each Other? The Complete Guide

Koi fish are one of the most beautiful and famous ornamental carp globally. Not only that but they are also known for their unique personalities and behaviors.

Thus, many first-time aquarists commonly wonder: Will Koi fish eat other fish?  if they release them with other species in a habitat?

Look for the answer no further than this article. It will show you the exact answer and the behaviors of these stunning carps. Let’s get started!

Will Koi Fish Eat Other Fish?

The short answer is yes! These carps will attack, kill, and eat other fish species, but that’s not always the case for all of them, at all times.

Many people regard these aquatic creatures as gentle species. They are omnivores and opportunistic eaters.

Like their cousin – the goldfish, this species can eat anything they put in their mouths. They even try to eat things that aren’t food, such as rocks.

If you raise these creatures with aquatic friends who are tiny enough, they will kill these species unless you provide them with plenty of hiding places.

However, they are not always aggressive. They will become violent against their fellows, mostly during mating season.

They may even attack and bite other males and females. These may lose scales or fins due to these attacks, putting them in danger.

Koi fish cannibalize their fry, so breeding them in a small pond with their offspring without interference might be challenging.

Why do they eat other mates? There are many theories around their behavior, but below are the main reasons. Let’s take a look!

They Are Hungry: These creatures are omnivores. They will hunt and consume other creatures, including their fry and spawns if you don’t feed them enough.

Overstocking Is Happening: If you keep too many pets in a pond without providing them with balanced food, they will fight each other for food.

At that time, overstocking will indeed occur. And these aquatic creatures opt for cannibalism rather than dying due to starvation.

They Make A Mistaken Identity: These carps can’t distinguish between their fry and insect eggs and their food, especially colorful pellets.

That’s why this species may eat tadpoles, but it’s their mistake. These food sources are not their favorites.

Are Koi Fish Aggressive? Koi Will Be Eating Smaller Fish?

Many people believe that Koi fish are aggressive, but this is not always the case. While it is true that Koi can be territorial, this is usually only the case when they are kept in a small pond or enclosure.

In larger bodies of water, Koi typically behave peacefully toward other fish. In fact, they are often used as part of a cleanup crew in commercial aquaculture facilities because they will eat algae and other aquatic plants.

So, while Koi may exhibit some aggression towards other fish in certain circumstances, this is not generally considered to be a major problem.

However, we still need to consider what creatures will Koi eat. Check the list below:

Fancy goldfish

When given the opportunity, Koi fish will eat these hapless goldfish.

This species is not the same as other common goldfish types. They are much smaller.

They also move slowly, making them ideal easy-to-hunt targets for giant Koi.


These are tough and bright species. They are much smaller than these carps, so they are not ideal fellows of these big Koi.


They are species that range in size from tiny to enormous.

They are tough species that can withstand a broad temperature range. However, they are incompatible with Koi, especially tiny ones.


Minnows are tiny creatures that can grow up to three inches in length. Because of their modest size, they have become an ideal diet.

They are among the toughest species, able to resist changes in water conditions, but their tiny size is a disadvantage.

Koi Fish Behavior

Like other pets, the behavior of your Koi may change from time to time.

Because pond carps live in water, determining the cause of the changes in their behavior might be challenging.

To make your task easier, below are some recommendations to check your carp’s behavior:


Usually, these carps would float around aimlessly, not bothering one another or the surroundings.

They’re suddenly pushing, jumping, flapping, and becoming more aggressive than ever if they’re breeding.

They may have an unusual odor. It appears that the spawning season has arrived! It usually occurs in May. However, it varies by region.

Breeding season


Since your pets are unwell, their behavior will change. Some diseases are easy to spot, but some may require a closer look at the carp or water.

For instance, if the carp require more oxygen due to insufficient aeration, they’ll jump out of the water.

In other cases, they may scratch on surrounding objects, gulp for oxygen, or clench their fins due to parasites.

Don’t worry too much! These diseases have treatments.


Generally, these carps don’t like playing hide and seek. If you notice them hiding, they may be in danger.

The common reasons that cause your pets to hide may include predators, water quality changes, new pond mates, sickness, or a new living environment.

Hiding behavior

Koi Fish Tank Mates

While these creatures will eat some species, they are still willing to make friends with certain types.

The creatures you plan to release in the pond should not be aggressive to avoid attacking Koi and be too small as these more giant carps will kill them.

These species should also share other things with Koi, such as care level or water quality and temperature.

Here are some species you can keep along with your big carp in a pond:


They’re one among the few species that get on well with Koi.

They can reach a maximum length of 4 feet, nearly the same length as Koi. Most barbels may reach 40 inches.


Tench are gentle and gregarious species that will get along swimmingly with big carp.

They can grow to be 70cm long and 7.5kg in weight, making them ideal mates of big carp.


These catfish may withstand a wide variety of temperatures. They can peacefully coexist with giant carp for a while.

Golden Orfe

One of the most friendly tank mates for Koi species is the golden orfe.

They have so many similarities that it’s difficult to tell them apart from golden carp while swimming.

If you want to know more about these creatures, you can watch this video:



Will Koi eat goldfish?

As described above, goldfish are smaller and especially Fancy goldfish. Though both Koi and goldfish are popular pond residents, Koi will eat goldfish if they are not the same size.

Some believe that Koi will only eat goldfish if they are starving, while others believe that Koi will eat goldfish under any circumstances. The truth is that there is no definitive answer, as each fish has its own individual personality and preferences.

However, it is generally advisable to keep Koi and goldfish separate, just to be on the safe side.

Are Koi fish cannibals? Do they eat small Koi fish?

It’s a common misconception that Koi fish are cannibals and will eat smaller fish.

In reality, Koi are not cannibals and will not eat other Koi unless they are sick or dying. Small Koi are actually more likely to be eaten by larger fish, such as bass or catfish.

Koi are omnivorous and will eat a variety of foods, including plants, insects, and small crustaceans.

In the wild, large Koi fish typically grow to be about two feet long. However, in captivity, they can grow to be much larger, with some individuals reaching lengths of four feet or more. Given their size and power, it’s no wonder that people sometimes mistake Koi for cannibals!

In A Nutshell

Will Koi fish eat other fish? They will kill and eat smaller species than them, such as Danios, Guppies, Minnows, or even Fancy goldfish.

If you want to keep other species in the same aquarium with Koi fish, it’s best to opt for species of the same size or larger than these carp.

Hopefully, this post will be helpful for you. Thanks for reading!