Koi Carp in Japan


Don visited Mr Masao Kato, a koi breeder in the Niigata Prefecture who has bred some of the best koi carp in Japan. His breeding farm is a huge property, with large breeding ponds stretching over hundreds of metres of land. Mr Kato has been breeding koi for about 40 years and, although by the size of his property it may appear that koi breeding is his business, it isn’t. This is a hobby for Mr Kato. A passion which is followed by many, many Japanese koi breeders.

A good fish can be worth around $AUS400,000. In fact, record prices have been close to one million dollars! Despite these incredible prices, many breeders would never consider selling their fish. However, sometimes when approached by other breeders or friends, breeders have exchanged carp on the condition that they have a pick of the offspring.


The word koi is not Japanese, but rather Chinese. Japanese call the fish Nishikigo (coloured koi). The fish are regarded as symbols of strength, good luck and prosperity in Japan. Due to the large numbers of colour variations, koi are sometimes thought to be different species, yet all are Cyprinus carpio, a member of the carp family. Koi breeding began in Japan in earnest during the seventeenth century in the rice-growing region of Niigata Prefecture. This is still the dominant koi breeding district in Japan.


Koi are bred to be viewed from above and koi with attractive colourations on the side are actually regarded as inferior. There are several colour varieties of koi with different names for each variety. No two koi will ever look the same and professional breeders go to great lengths to breed their fish based on six main varieties of koi patterns and colours. For the hobbyist, the variation is limitless. Some of these varieties include;

  1. Kohaku: A koi with a white body and red pattern on the back. This is the most popular variety of koi.
  2. Tashio Sanke: A tri-coloured koi with a white body, red pattern and black accents on the back.
  3. Tancho: A koi with a red spot on the top of its head, and no red on its body.
  4. Ogon: An entirely solid-coloured fish such as solid gold.

The average Koi can grow from 60cm (24′) – 91cm (36′). However, as Don found out, exceptional fish can grow to be around one metre long. The size of the pond, the amount of aeration and feeding methods will all combine to affect the growth of the fish. For those hobbyists, it is not uncommon for a small koi to grow 5 – 10 centimetres a year in a backyard pond.

To most western hobbyists, the more vivid and intense the colour of the fish the better it is. The Japanese rather look for purity of colour rather than intensity. If a fish is white and red, the red must be uniform, it doesn’t matter how deep the red is as long as it is one shade of red. Edges must be sharply defined.


In Japan, the fish are fed once or twice a day, depending on the season. In warmer temperatures, the fish will be fed more frequently. Koi are naturally bottom feeders but are fed specially prepared pellets in elaborate breeding tanks.

Ponds and tanks

Ponds are not heated, but the water is constantly aerated and filtered. The fish can withstand a wide range of temperatures, however sudden changes in temperatures are undesirable. Koi can even survive under the ice in extreme cold as long as the water does not freeze solid.

A very serious breeder, such as Mr Kato, will easily spend a quarter to half a million dollars worth of pumps, biological filters, canister-type filters and aeration. Breeders will also go to extraordinary lengths to control the acidity of the water, the amount of ammonia and other chemicals present in the water. The water quality is strictly monitored and movement of water is controlled everywhere to produce the healthiest fish possible; some of the healthiest fish Don has ever seen.

Health and lifespan

Koi are remarkably hardy and healthy fish. This has contributed to their dominance over many native species in rivers and tributaries in countries where they have been introduced such as Australia. Japanese breeders say smaller koi have a much higher mortality rate than larger koi and are more susceptible to diseases and changes in the environment. However, healthy koi can live for up to 50 years. In Japan, 70 year old koi are not uncommon.


Koi are relatively easy to breed but cannot be bred in a regular aquarium setup due to the large amount of fry and numbers of adults required in the one tank. They can lay thousands of eggs in a single breeding. In Japan, koi are at least three to four years old and of sufficient size before they are bred. The female is ‘fed up’ at the beginning of spring using shrimp and koi pellets in order to increase her capacity to breed.

Two or three males are put in with a plump female and the water temperature is slowly brought up by 3°C to expedite the breeding process. Once the fish have spawned (in about 3 to 7 days) they are removed from the pond and the fry should be raised separately from their parents.


Very large competitions are held each year throughout Japan where breeders take the best of their stock to be judged in large pools which also contain their competitors koi. Judging is based on perceived beauty and each judge will have his own scale of judgement. The way a fish swims or carries its fins may impress one judge, who may overlook defects. In the 1950s, judging was based on a 100-point system. Points were deducted for faults relating to body shape, colour pattern and colour. In the 1980s this criteria was changed to giving points for special characteristics, making it possible for fish with outstanding colour to win a contest even though it had serious flaws in size of pattern.

Further information

Koi breeding is not beyond the capabilities of hobbyists in Australia. However their occurrence as a pest species means that koi cannot be kept as ornamental fish anywhere other than NSW and WA.

A good beginner’s guide to keeping koi is;
Koi: A Complete Pet Owner’s Manual
RRP $19.95, by George C. Blasiola
ISBN 0812035682
Published by Barron’s Educational Series
This covers all aspects of keeping and caring for koi.