About koi

Japanese koi
They come when called, follow their owners as they walk around the pool, allow themselves to be petted, and will take food from outstretched fingers. They’ll outlive almost any other kind of pet, maybe even you. They don’t bark, or bite, or tear up the garden.

They’re carp (Cyprinus carpio) not gold fish, which are only relatives. But they have common names more descriptive of their magnificent colors or patterns, living jewels, flower koi, brocade koi, fancy koi. They’re also called samurai or warrior fish, but not because of their belligerent or fight among themselves. Rather, it’s because of their reputation as strong, determined swimmers able to negotiate rapids and ascend waterfalls. Carp have long been associated with success masculinity in China and Japan. In Japan, on May 5 Celebrations of Boy’s Festival Day households fly cloth and paper carp kites, one for each boy in the family.

Before 800 A.D. common carp were cultivated in Japan (even earlier in China) for food. Carp were bought to North America in the 1870s. A few offspring of the common carp developed bright colours. This intrigued some Japanese, especially rice and cattle farmers in an isolated mountain area northwest of Tokyo, now Nigata Prefecture. In the 1800s breeding and selecting became an intensive and highly competitive pastime for the farmers in their off hours and when snow stopped normal work. Each man tried to out do his neighbor by developing fish more dazzling in colour or unusual in pattern. Interest in carp breeding didn’t reach the outside world, however, until 1914 when some colourful specimens were exhibited in Tokyo and several were given to Crown Prince Hirohito. Such fish had never been seen before outside the villages of the carp-growing region.

Koi are carp in one, two or three colours
Nishikigoi is a general term for coloured koi with markings which are bred for appreciation. During the Second World War the authorities did not approve of the words Coloured or Flowery, so it was renamed Nishikigoi. The word “koi” was first used about 2500 years ago in China, it was in 533 B.C. when Confucius’ son was born and was presented a fish by King Shoko of Ro. The fish was named “Koi”.

The fish also get Japanese names for their colours. One-colour koi are; white (‘Shiro-muji’), red (‘aka-muji’), yellow (‘Ki-goi’), gold (‘Ohgon’), orange (‘Orange-Ohgon’). Single colour koi are not only differentiated by colour but also by whether the colour has a flat or metallic appearance. If the colour designation is followed by ‘Ohgon’ (or ‘Ogon’) it’s metallic. Koi with two colours; red on white (‘Kohaku’), black on white (‘Shiro-bekko’), white on black (‘Shiro-utsuri’), black on red (‘Aka-bekko’), yellow on black (‘Ki-utsuri’), and blue on top with orange or red underneath (‘Asagi’). Here bekko means tortoise shell, ‘utsuri’ means reflection. The three-colour koi are either white with black and red motties (‘Taisho-sanke’) or black with white and red motties (‘Showa-sanke’). ‘Sanshoku’, which means three colours in Japanese, may replace ‘Sanke’ in a name.

Besides the variation in colour and pattern, there are also variations in scale formation. Some koi have typical carp scales, other called ‘Doitsu-goi’ (German carp) have rows of large scales or are scaleless.

Care and feeding of koi
Despite their exotic colouration, koi are not tropical fish. They’re surprisingly hardy and can be raised outside in all but the very coldest climates. They adapt to water temperatures between 4 deg C and 32 deg C, through 18 C and 21 C is best for maximum growth.

When water freezes the main precaution is to keep an opening in the ice for oxygen. Koi are heavy users of oxygen, especially at night and in warm temperatures. Some form of aeration of the water such as a waterfall or bubbler may be needed, particularly if the pool is crowded. Koi will eat both animal and vegetable foods, either fresh or dried. They require a balanced diet for fast growth and most brilliant colouration.

Pet shops mainly sell prepared koi food that you can supplement with shrimp, crab, various worms, bits of meat, lettuce, cabbage, carrots, watercress, and cooked egg. Koi owners seem to have their own special menus. You feed about the amount your fish will eat in five minutes, taking care not to overfeed.

Meal time is once in the morning and again in the late afternoon, though some owners feed once a day.

Overfeeding tends to foul the pool water with uneaten matter that sinks, decomposes, and encourages the formation of algae. Many koi owners use pellet food that floats. It encourages the fish to come to the surface to eat, and uneaten pellets don’t sink. When the water temperature goes above 32 deg C or below 4 deg C stop feeding. The fish aren’t active then and require little or no food, though some lettuce twice a week is beneficial.

Pool size and water clarity
A koi pond can be any size or shape. However, depth is important – no shallower than 45 cm and ideally between 60 cm and 1 metre, or deeper. It also must be large enough so that fish have room to swim – at least 3 metres across. An ideal pool would be concrete with a 20 cm thick base and 15 cm thick walls. It would have shallow places for feeding and fish watching and deeper water where the fish can go when surface water heats up or starts to freeze or to escape a predator like the family cat. Koi don’t mind a change in water temperature fluctuation if it’s gradual. Place the pond where it gets some shade. This is both good for the fish (colours tend to be richer and deeper in shade) and will also keep down the algae.

If you really want to enjoy your colourful koi, pond water should be as clear as possible. It’s not that koi necessarily prefer clear water; after all, in nature they’re bottom feeders in lakes and streams. But domesticated koi seem to be bothered less with pests and diseases in clear water.

One reason is you can spot a problem before it gets out of hand. Water filters will keep pond water clear. But we’ve seen ponds that are absolutely crystal clear and have no filters. Water is simply circulated so that fouled water is naturally forced up a pipe from the bottom and flows out over a spillway.

A natural filter method using the roots of water plants works like this; water from the main koi pond is pumped to a waterfall that pours over a hillside. It is aerated as it spills down over rocks into a smaller pond with water lilies. Here larger particles of debris settle out to nourish the lilies, and the cleaner water passes over a spillway and travels down a 5 metre long, 15 cm to 20 cm deep stream bed filled with water hyacinths. A fantastic root network traps even more debris. This nourishes the water hyacinths and encourages good blooms.

Small crustaceans introduced into the stream with the water feed on algae that otherwise would make the water green. This kind of natural filtration system is difficult to design and construct, so you may choose to rely on a pump and filter system; however, these will require weekly cleaning.

Some koi owners have made their own filters using gravels of different grades; these are called biological filters and are by far the most popular in Australia. A power failure of long duration can mean trouble, especially if a pond is fairly heavily stocked with koi. If it happens, you can use a battery operated pump to oxygenate the water.

Article by H. Watson