The World of Koi

Addictive hobby can instantly beautify any outdoor space.
Photo: David Croxford

The sound of the water is the first thing you notice — constant yet calming. The waterfall and pond eventually come into view in the Nuuanu home’s terraced backyard, which is welcoming, green and lush. Hold on. What’s that flash of color? It’s koi — a stunning yet serene addition to this tropical oasis.

“When you’re around them, there’s a real calmness that koi exude,” says Bob Armstrong, who refurbished this koi pond when he bought the Nuuanu home in 1993. “They’re beautiful, graceful and people can’t take their eyes off of them.”

Indeed, it’s nearly impossible not to be mesmerized by koi — a domesticated type of the common carp. “People will be out shopping at Ala Moana Center, see the koi and they just stop and stare,” says Dr. Andrew Rossiter, director of the Waikiki Aquarium. “Sitting next to the water and watching koi is very therapeutic, very relaxing. They’re one of the few fish that live together with no aggression. They don’t dart, they just glide.”

With a little work, you, too, can experience the joys of koi in your own backyard. Koi are fairly easy to keep and provide a constant display of color; but, beware, collecting them can get expensive fast.

“It would not be out of the ordinary to have a pond with more than $100,000 worth of fish in it,” says Rossiter, who once saw a collector pay $32,000 for a rare koi. “You can spend $10 on a 4-inch koi or $1,000, the choice is really up to you.”

Since first seeing koi when he was 16 years old — he thought they were giant goldfish — Rossiter has been an avid fan of the fish. Well, maybe avid is an understatement. After much effort convincing his wife, he converted their backyard pool into a koi pond. “It took me two and a half years and a car to persuade her to let me change it into a pond,” laughs Rossiter, who has been interested in koi for more than 40 years. “But we’re still married.”

Today, Rossiter has 40 koi in his home pond, with 30 more on the way from Japan. “They make excellent pets for a variety of reasons,” he says. “They don’t shed fur, you don’t have to walk them, they’re not noisy, they’re easy to feed and they live a long, long time.”

And Hawaii’s climate makes it one of the best places in the world to keep koi, which have an average life expectancy of 20 to 30 years. “It’s one advantage we have over Japan,” says Rossiter. “Because we don’t have winters here, koi can be fed right through the winter. The more they eat, the faster they grow. When it’s too cold, they go into a state of hibernation and stay at the bottom of the pond.

“Plus, you get to be outdoors next to your pond year-round.”

For those who want to start their own koi ponds, it’s important to invest in a quality filtration system, routinely maintain water quality and find a reputable koi dealer. Do your research and plan ahead.

Knowledge is power, says Rossiter. “The biggest mistake people make is spending lots and lots of money on fish, then not having an adequate filtration system to handle them,” Rossiter says. “The second-biggest mistake is taking advice from people who really have no business giving advice.”

Also, be wary of gadgets. “Technology has advanced way beyond what’s necessary,” he says. “Something can have lots of bells and whistles, but sometimes a bucket and sponge will do exactly the same thing.”



Ideally, it should be 6 feet deep and 10 to 30 feet across. “It’s important to think about the type of pond you’re going to have,” says koi owner Bob Armstrong. “The pond will determine how big the fish are going to get.”


There should be sufficient sun in the morning – the sun allows the generation of oxygen.


75 to 80 degrees Fahrenheit.


Koi are omnivores and will eat practically anything that humans do, but overfeeding can lead to health problems. Koi should be fed every three to four hours.


Filtration and purification are vital. Lack of oxygen can be fatal.


Healthy koi swim freely all over the aquarium and often come rushing when it’s feeding time. Sick koi will gather in one place and hardly move.


(gallons per Koi)

Small Koi (2” to 8”) 100 – 150 gallons
Medium Koi (8” to 14”) 250 – 300 gallons
Large Koi (14” to 24”) 400 – 500 gallons
Jumbo Koi (24” to 36”) 750 – 900 gallons


QUICK TIP: For each koi, there should be 250 to 300 gallons of water in your pond.



With red patterns set against a white background, the Kohaku are quite sensitive to water conditions.

Taisho Sanke

Sanke for short, this common variety has a white body with red and black markings.


Has a black body with red and white markings and is a hardy fish that does well in most ponds.

Koi appreciation consists of three major points:

  • Body Conformation – Its size and shape. Ideally, it should be full with a rounded shape.
  • Quality – This refers to the koi’s skin.
  • Pattern – What sets it apart: A dynamic, well-balanced pattern catches the eye. No two koi are exactly alike.
Categories: Outdoor Living