Do Koi Fish Eat Other Fish? {Top 6 Fish To Keep With Koi}

When I keep other fish with my koi in the same tank, I tend to worry about size differences. Are you wondering do koi fish eat other fish?

Do you want to know if it’s worth the risk to keep koi fish with other fish?

This article contains details on koi fish and their relationship with other fish.

Do Koi Fish Eat Other Fish?

Yes, Koi will feed on small fish that easily fit into their mouth. They will typically eat fish fry, even their own.

You cannot wholly classify koi fish as aggressive fish as they are only aggressive to certain fish species. They will attack some fish, and their bite can be lethal to the fish.

They are not aggressive towards their fellow koi fish but will only show their aggressiveness towards one another during breeding seasons.

Do Koi Eat Other Fish

Are Koi Fish Aggressive?

Koi fish are not known to be aggressive. They are usually gentle and easy going. The aggression that you are noticing could be due to bullying because they are realizing they are larger and are able to push smaller fish around.

Koi fish can eat fish fry and it’s best to keep them with only fish of other species in the pond that are similar to their size or large enough that they cannot fit into the mouth of a koi fish.

Is your pond overcrowded? If so coy fish may act a little more aggressive. Stress leads to aggression and so do these factors below:

  • Overstocking And Insufficient Space
  • Diseases Or Injuries
  • Water Quality Problems
  • Food of Poor Quality

If you would like to prevent your koi fish from being aggressive, you can try the following recommendations:

  • Maintain High Quality Pond Water
  • Quarantine Aggressive Fish Newcoming fish for 1-2 weeks. 
  • Examine The Health Of Fish Regularly
  • Provide Plants For Added Hiding Spaces. 

What Kind of Fish Can You Put with Koi?

As much as koi fish will delight in attacking some fish, they will gladly allow some other fish to stay with them in the same tank.

  1. The fish you keep in the tank should not be aggressive to prevent them from attacking koi fish.
  2. They also have to be large enough to prevent them from being feasted upon by koi.
  3. The fish should have the same temperature requirement as koi fish so that both fish species will thrive at the same temperature range.
  4. The fish you are adding to the tank should have the same care level as koi fish. The fish must not be a competitive eater to prevent it from fighting with koi for food.
  5. Ensure the fish is of the same size as the koi; keep small fish with small koi and large fish with large koi.
  6. It is better to keep a bottom feeder fish with koi fish to prevent the troubles of feeding.
  7. It is also better for the fish to have the same characteristics as koi fish to increase their compatibility.
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Top 6 Fish To Keep With Koi

  1. Barbels
  2. Catfish
  3. Pleco
  4. Goldfish
  5. Tench
  6. Golden Orfe

1. Barbels

Barbels are one of the few fish that can live peacefully with koi fish. They are almost the same size as koi fish and can grow to about 4 feet, with most barbels growing to 40 inches. They are bottom-feeder fish and clean the bottom of the tank by eating up leftover foods by koi fish.

2. Catfish

Some species of catfish will live with koi fish in the same tank. They include Columbian sharks, iridescent sharks, bumblebee catfish, bandit cory fish, etc. These catfish types can tolerate a wide range of temperatures and happily live with koi fish for a specific age.

3. Pleco

Plecos are tropical fish with hardy characteristics. They can live in ponds and aquariums with high compatibility with koi fish. They are colorful fish that will stay well with koi fish, but you have to keep the water higher than 55 degrees Fahrenheit as they won’t thrive at that temperature and below.

4. Goldfish

Goldfish are compatible tankmates of koi fish as they have the same characteristics. They are coldwater fish with almost the same diet as koi fish making them suitable tankmates. Not all goldfish species are compatible tankmates with koi fish, so you should stay away from them (like fancy goldfish).

5. Tench

Tench are peaceful and social fish that will pose no issue when kept with koi fish. They can reach up to 70cm and weigh up to 7.5kg, making them one of the perfect koi fish sizes. They are bottom feeders and will tend to disturb and disrupt the bottom of your tank.

6. Golden Orfe

Golden orfe is one of the most compatible tank mates of koi fish. They have similar characteristics that you can barely differentiate between them and golden koi fish when swimming. They are bottom feeders that require to be kept in groups of at least three.

Other fish will live peacefully in the same tank as koi fish. You only have to check their characteristics to know which fish fits best for your koi.

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List of Smaller Fish That Koi Will Eat

When stocking fish with koi fish, do not make the mistake of stocking smaller fish. Koi fish will attack and feed on them. Here is a list of smaller fish koi will eat when they cross paths;

Fancy Goldfish

Fancy goldfish are part of the unlucky fish that koi fish will feed upon when they get the chance. Unlike common goldfish, fancy goldfish are smaller and are not a good choice to stock with your koi fish. They are also much slower, making them an easy target for koi fish.


Minnows are small fish that grow to a maximum length of 3 inches. Their small size makes them part of the menu of fish for koi. They are one of the toughest fish with the ability to withstand fluctuations in water elements, but their small size creates the setback.


Guppies are colorful fish with hardy properties. They have small sizes with an adult growing to about 2.5 inches long. Their small size makes them an easy meal for koi fish and not a suitable tank mate for them.


Danios are fish species with a wide range of body sizes, from small species to giant danios. The giant danios grow to about 5 inches long, which is still small enough to win an attack from some koi fish. They are hardy fish and will tolerate a wide range of temperatures, but they are not compatible with koi fish.

There are several other fish that are not compatible with koi fish. If the fish is smaller and probably tastier, you should not feed them to koi fish. You can also pick bottom feeders over others as they will likely not move around the koi fish mouth.

Are Koi Fish Cannibals?

Koi fish are not complete cannibals due to some reasons. The first time you will experience cannibalism is when they are smaller, in their fry stage. When they start growing, they do not grow at the same time. The bigger fries will end up eating their smaller siblings.

The other time you will notice cannibalism is when adult koi fish eat small fries. They eat them not because they are aggressive but because they cannot differentiate between their small fry and other small fish.

The fries are small, and they resemble small aquatic animals that koi feed on; it makes it difficult for the koi to place a difference.

They are not full-time cannibals; they only exhibit once in a while. They will not eat their babies when they grow to the stage they can identify them and will not feed on each other in their adult stage.

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How to Prevent Koi from Eating Smaller Fish

There are several ways you can prevent your koi from eating smaller fish. They include;

  • Add pond plants to serve as hiding space for smaller fish.
  • Do not put too many fish in a small place.
  • Always give your koi fish an adequate amount of food to keep them from being hungry and feeding on smaller fish.
  • Provide small pond insects and zooplanktons as an alternative for your koi fish to eat.
  • Keep smaller fish away from the same tank as large koi fish.
  • Provide demarcation in the tank to keep the small fish from the large koi fish.

Frequently Asked Questions:

1. Do koi fish get aggressive during breeding season?

During the breeding season, koi fish will bully and bite females and other males. These bites can cause the fish to lose scales and fins, which can, in turn, cause them great harm. Koi fish do not need to be in breeding seasons before they attack and kill other fish.

2. Which fish get attacked by koi fish?

Fancy goldfish are common victims of koi fish attacks as koi will always attack them when they come across them. Fancy goldfish are not only the victim on the list; other small fish will also face attack from koi fish when they cross paths.

3. Can angelfish live with Koi?

Angelfish can live together with koi, but that should not happen in the first place. Angelfish need warmer water to thrive, while koi fish need colder water. Koi fish will need large ponds, while angelfish do not require that much space.

4. Can I mix goldfish with Koi?

Koi and goldfish are peaceful fish and will live peacefully together. However, it is not all goldfish that you can keep with koi fish. Smaller species like fancy goldfish are not suitable tankmates for koi fish.

5. Will Koi eat small Koi fish?

Big koi will
not eat little koi; thus, the koi is recognizable as a koi fish. They will only eat them in their fry, where it is difficult to differentiate them from other small aquatic animals. They are opportunistic feeders but will try to avoid small fish.

6. Do Koi eat goldfish?

Koi fish will not eat goldfish as the goldfish is a suitable tankmate. Some species of goldfish, like fancy goldfish, are not suitable tankmates of koi fish. Koi fish and common goldfish will like the company of one another.


Koi fish will eat other fish if they are small and can fit into their mouth.

Although they will not feed on their kind, they will sometimes eat their babies when they are small due to understandable reasons.

Koi fish are not very aggressive, but they cannot help their opportunistic appetite from eating smaller fish.


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Hello, I'm Jason. I'm the guy behind I volunteer at my local fish shop and I created this site to offer tips and advice on the fish I care for.