Koi Fish: Shining Jewels of the Water Garden

Koi fish swimming in pond
The Kohaku ("red and white") is one of the most commonly collected and popular breeds of koi fish. Pieter in Japan/Flickr (CC By-SA 2.0)

Certain animals just seem to have really great PR teams hyping up their reputations. Elephants? Supposedly have steel-trap memory banks. Dogs? Well, we all know dogs are just perfect. But koi fish? No one ever really raves about koi fish.

And yet, the colorful swimmers are definitely deserving of admiration — while they may not be A-list celebrities like some other species, they've got a lot going for them. "[They are] not only a pet, but also art," says Taro Kodama, president of Kodama Koi Farm. "They are called living jewels — beautiful as one koi, even more beautiful as a group."


"They are beautiful, gentle, docile fish that are relatively easy to maintain with the proper space, water filtration and food," says Laura Hilstrom, Aquatics Lead in the Department of Herpetology & Ichthyology at the San Diego Zoo. "Koi can be easily trained to eat right out of your hand. Watching koi swim can be both a mesmerizing and calming experience and koi keepers are known for taking great pride in the care of their aquatic pets."

Here are just a few fun facts about these beautiful, resilient, aquatic superstars.


1. Japanese Koi Fish Humble Beginnings

Koi fish are what you might call a happy accident. In the 1600s, Japanese carp farmers began noticing unusual color variations among the fish. "The popular koi fish of today are actually ornamental varietals of domesticated carp," Hilstrom says. "Black carp originate from China and were first bred for red color mutations (noted around 720 C.E.) that were originally developed into the many fancy goldfishgoldfish varieties. Soon after, colorful varietals of black carp were being kept by Japanese emperors and nobility."

While koi were originally bred for consumption, like all other carp, farmers began breeding them exclusively as pets in the 1800s, thanks to their uniquely stunning appearance. By the 1900s, farmers were breeding koi in the United States, England, and Europe, and by the 1960s, koi were considered coveted pets all around the world. According to the San Diego Zoo, people on six out of seven continents now keep koi as pets.


"The Japanese referred to the colorful carp as nishikigoi, meaning 'braided or brocade,' in reference to the colorful textiles of the country," Hilstrom explains. "These nishikigoi varieties are what westerners now refer to as koi fish. Koi became popular in Japan in the 1820s and then popular worldwide in the early 1900s after being part of an exhibition in Tokyo, Japan. It has since blossomed into the popular hobby fish culture of today with many more brilliant color variations."

2. What Do Koi Fish Eat?

There are a lot of reasons koi make great pets, but here's one: They're not picky when it comes to food. The omnivorous fish will snack on everything from snails and insects to algae and plants — they'll even nibble on fruit. But if you're keeping koi as pets or you've seen them on display, you probably know there's specially formulated food to meet their nutritional needs. The food is also designed to float so the fish come up to the surface to feed, delighting spectators in the process. And, consider this bonus for jet-setting pet owners: The beautiful swimmers don't have to eat very often. "No need to feed them for weeks — they eat algae on the wall," says Kodama. "So unlike dogs and cats, you do not have to worry about them while you are on vacation."


3. Koi Fsh Colors

Red is the koi's signature color, but it's not the only shade the species rocks. There are actually various types of koi that come in all hues, including orange, yellow, black, white and blue. "There are more than one hundred varieties in koi, but they are all the same species," Kodama says. "They are carp, they just have different looks." It's true — there are over 100 different types of koi, but here's a brief breakdown of some popular varieties:


Types of Koi Fish

  • Asagi: These have either a blue or indigo body, and red at the base of their pectoral fins (called Motoaka).
  • Bekko: The name of this type translates to "tortoise shell," and you can find it in shades of red, yellow or white.
  • Butterfly/Hirenaga/Longfin: This type of koi is named for its graceful, flowy fins.
  • Kohaku: This is considered the most representative variety of koi and is known for its signature red pattern on a white body.
  • Yamabuki: These metallic-tinged fish look like swimming pieces of shimmering gold, and they're said to represent wealth and prosperity.
Koi fish in a splashy palette of colors
Ornamental koi fish come in over 100 varieties, which can be mixed to create a splashy palette of color in the garden pond.

"Koi originated from the species Cyprinus carpio, the common carp," Hilstrom says. "There are only a few species and subspecies of koi carp based on their locality, but the color varieties of koi top 200 or more. Color varieties are based on coloration, color patterns, and scale patterns. For example, the popular Gosanke koi includes Kohaku, Taisho Sanshoku Sanke, and Showa Sanshoku varieties."


4. Koi Pond Size

Koi are pretty big fish that require a lot of space (the "big fish, small pond" thing doesn't work for them). With the right care, koi can grow to be between 2 and 3 feet (0.6 and 0.9 meters) in length and some varieties, like the Chagoi, can be even bigger — up to 4 feet (1.2 meters) long. If you're looking to keep koi as pets, just know you'll need to make room for their growth; little ones can live comfortably in large indoor aquariums, but will eventually need to be transferred to a large pond. Koi aren't lightweights either — they typically tip the scales around 35 pounds (16 kg), and experts advise filling a pond with about 500 to 1,000 gallons (1,893 to 3,785 liters) of water per each adult koi.


5. Koi Lifespan

If you're looking for a pet with longevity, the koi might be a good option. Most koi have a lifespan of about 20 to 30 years, and believe it or not, it's been reported that some have lived for more than 200 years (which may be a longer-term investment than you meant to take on). To increase the odds of your koi staying alive for decades, you'll of course want to keep it healthy with properly filtered water and solid nutrition. Make sure they're as unstressed as possible too, by keeping their environment uncrowded and free of parasites and toxic chemicals.


6. Koi Fish as Pets

Love the loyalty of a pup but just can't make the commitment? O.K., so a koi fish isn't exactly snuggly, but experts say you can train them to eat out of your hand, so that counts for something, right?

"Yes koi can be trained to eat out of your hand," says Casey LeFever, co-owner of Next Day Koi. "It's all about acclimating them to your presence by the pond or tank. To your fish, you look like a hungry predator when you hang out around the side of the pond. Start by throwing some food in while sitting nearby, but not reaching into the water. They will slowly become acclimated to your presence and you can work your way closer, eventually close enough to stick your hand in the water. Once they learn your hand is not a threat they will come up and eat food out of your hand. There are floating food rings that can help to keep the food close to the edge of the pond."


It's true, the fish has to feel very safe and secure in order to be comfortable enough to nibble out of your palm, so slowly getting them accustomed to your presence is key — and the type of koi you try to train can matter too. "Make sure you have at least one friendly variety such as Chagoi, Soragoi, Ogon, or Karashi," Kodama advises. "Feed them Manda Fu, a special food for hand-feed training."