Koi fish are one of the most popular and colorful forms of the Amur carp species. They are often referred to by their Japanese name, Nishikigoi. Nishikigoi means “swimming jewel.” The Koi fish originates from the early 19th century. During that time in Niigata, Japan, they began breeding the Koi fish from the Amur carp species.

Japanese culture and tradition have a special relationship with the Koi fish. They symbolize strength and success for a long time. With the average lifespan of a Koi fish being over 20 years and some Koi living for more than 70 years, they also are symbols of health and longevity.

Multi-colored Koi fish swimming in a pond.
Multi-colored Koi fish swimming in a pond.


Appearance

The appearance and color of a Koi fish vary depending on the type. Most carps seen in rivers and streams tend to be brown or light brown, but Koi come in a variety of colors. The more traditional colors of the Koi are white, black, red, and orange. But with over 100 different types of Koi and selective breeding, there are yellow, blue, cream, and metallic colored ones.

The size of an adult Koi can vary from 1 to 2 ft. long. With an average weight of 35 pounds. This makes the Koi fish one of the more robust, durable species of river fish. Koi Fish have large scales, and the fin on their back is elongated and sunken in their closed spine.

Gosanke variants are the most popular Koi fish.
Gosanke variants are the most popular Koi fish.

The most popular and commonly seen Koi would be in the “Gosanke” category. Which is comprised of the Kohaku, Snake, and Showa variants. Kohaku is a type of Koi with a white body and red pigmentation.

Their white and red bodies create a sharp contrast. Sanke means “tri-colored” and is a Kohaku type with black marks included on the body. Showa Koi are very similar to the Sanke type with the same coloration. But Showa Koi have more black pigment than red, creating a different contrast to the Sanke.

Habitat

Being an ornamental fish, Koi are usually kept in large ponds. While being a coldwater fish, they actually benefit from being kept in the 15-25 C. (59-77 F.) range. Long exposure to cold, winter temperatures can negatively affect their immune system. It’s also essential to keep Koi ponds clean with high-quality water. This can be achieved through filtration systems designed for Koi ponds.

A Koi fish surfacing for food.
A Koi fish surfacing for food.


Diet

Koi fish are omnivorous, and their diet must be varied with different fresh vegetables to keep a healthy balance of nutrients. Koi fish are naturally bottom-feeders, but most of their food is designed to float to the surface. This is to encourage them to the surface in case they need to be checked for parasites and ulcers.

During the wintertime, if the water in their habitat falls below 10 C. (50 F.), feeding is not recommended. Their digestive systems slow down immensely, and they eat very little. They normally feed upon small bits of algae during this period.

Threats

The main threat to Koi is predators such as; herons, otters, raccoons, cats, foxes, and badgers. The bright colors of the Koi put them at a huge disadvantage to these predators. To best protect a Koi habitat, it may be necessary to string nets or wires above the surface.

The two main health concerns among Koi are the koi herpes virus (KHV) and rhabdovirus carpio, which causes spring viremia of carp (SVC). No treatment is known for either disease.

Two Koi's in a green pond
A traditional Koi pond


Reproduction

The natural breeding season for Koi is in spring and summer. Females will reproduce for the first time between four and six years old, and males between three and five years old. The male will initiate things by following the female and giving nudges. They then attach their sticky eggs to water plants or any object submerged in water.

Once Koi fish hit the age of maturity, they will reproduce every year. Females can produce hundreds of spawn, but many of the fry do not survive due to being eaten by others. On average, the fry will be hatched in four to seven days.

Koi Fish Facts

  • The scientific name for Koi is “Cyprinus rubrofuscus.”
  • In July 1974, a scarlet Koi named “Hanako” was reported to be the oldest known Koi at 226 years old.
  • Koi are considered to be an invasive species in many areas. They can reduce the abundance of aquatic plants, and make the water unsuitable for swimming or drinking.
  • Koi fish are commonly misconceived as large goldfish, with both being domesticated from carp.
  • Koi fish were initially bred for eating purposes, and it wasn’t until the 1800s that the fish was bred as an ornamental pet.


FAQs

What is the life expectancy of a Koi fish?

The average lifespan of a Koi fish is 20 to 40 years, with some Koi living past 70 years. They check the age of Koi by studying the growth rings on their scales.

How much does a Koi fish cost?

The cost of Koi fish depends on a lot of variables; color and pattern, genetic lineage, body shape, size, age, and sex. The more affordable Koi range from $8 to $10 dollars, and the most expensive can cost up to $200,000.

Why are Koi fish considered special?

Koi fish have close ties to Japanese culture. Symbolizing good luck, prosperity, and longevity. They have been characterized for their durability and beauty.

What type of fish is a Koi?

Koi fish are brightly colored, ornamental types of Amur carp. They were first bred in the early nineteenth century in Japan.