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Can Koi Fish Live in Tanks? Vet Approved Size & Habitat Tips

Chris Dinesen Rogers

By Chris Dinesen Rogers

school of koi fish in water

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Dr. Lauren Demos

DVM (Veterinarian)

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People have raised Koi fish or Nishikigoi for centuries as both food and ornamental fish. Over 100 varieties exist. You may know them as colorful additions to a water garden or pond. The native species is the Amur carp (Cyprinus rubrofuscus), a drab and plain-looking fish. Some consider it a subspecies of the Common Carp (Cyprinus carpio). Selective breeding has yielded the colors and variations you’ll find.

Learning its origin can help answer the question of whether you can keep Koi in a tank. This fish can get over 28 inches long and over 8 pounds by the time it’s 7 years old. The answer boils down to whether you have the space to raise Koi indoors. We’re talking about a minimum tank size of 75 gallons or more. That’s an aquarium measuring 48 inches L x 18 inches W x 21 inches H.

The short answer is that Koi can live in a tank. However, they are unlikely to thrive in the long term without the necessary space to move and grow.

aquarium plant divider

The Natural History of the Koi

Several factors are strikes against keeping Koi indoors. Of course, breeders likely raise young in tanks if only to keep them separate from larger fish that might eat them. We mentioned size being an issue. We’ll delve deeper into that matter later. However, it comes into play when you consider reproduction. This species is polyandrous. That means one female may have several males. In other words, you must have at least three fish in your tank.

This species lives in small schools as part of its social structure. Even a 4-foot x 6-foot pond will hold roughly 250 gallons, plenty of room for a small number of Koi. That’s about 2,000 pounds of water, not counting the tank and everything in it!

koi garden pond
Image Credit: Ravi Mohan, Pixabay


Koi are coldwater fish. They prefer water temperatures below 75℉. Some can even live outdoors year-round. Warmer temperatures increase the risk of bacteria development. You also must think about the Koi’s habitat. It lives in many different habitats in nature. However, it prefers the bottoms of waterways since it roots around in the substrate looking for invertebrates, insects, and mollusks.

Replicating this environment in a tank would likely be challenging. Bear in mind that Koi fare best in ponds that are at least 24 inches deep. We’re talking about a massive tank for a fish that can live over 40 years in captivity. Therefore, we must circle back to whether keeping Koi in a tank is practical. The answer is getting murkier and murkier.

Size Influences

Let’s consider the fish itself. Several things can influence how big your Koi will get. First, we must think about its genetics. Color isn’t the only thing that selective breeding affects. Then, there’s the size of its aquatic home, whether it’s a pond or tank. It will directly impact how big your Koi will grow. The size of your tank is, in turn, influenced by the number of fish in your aquarium.

The Koi, like goldfish, isn’t the neatest of eaters. It’s downright messy when it forages for food. Keeping their water clean is difficult no matter where you keep them. All these things affect water quality. While the Koi is remarkably tolerant, it’s not immune to bacterial infections, low dissolved oxygen, and high ammonia levels.

If you think you can get by with a smaller tank and upgrade later, think again. This species grows rapidly. The Koi can grow over 9 inches long during its first year with proper nutrition. That’s a lot of fish food!

Image Credit: Vital Safo, Shutterstock

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Final Thoughts

Koi are beautiful fish and a welcome addition to any backyard pond. They are hardy and may even learn to take food from your hands. They are easy to take care of, with space being their primary requirement. Many other species will do so much better in a tank. You can even put goldfish on your shortlist. In the end, keeping Koi in a tank is best as temporary housing before you set up your pond.

Featured Image Credit: FOX, Pexels

Chris Dinesen Rogers

Authored by

Chris is an experienced pet writer specializing in science topics, with a particular passion for health and the environment. She has been a writer for over 15 years and lives with her husband and three cats in Michigan. Beyond writing about cats and dogs, Chris loves to learn about wine. She has WSET 1 and 2 certifications and is currently pursuing her Certified Wine Specialist Award (CSW).

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