The word Koi was first used in China to describe Carp and later became the English name for the Japanese fish called Nishikoi. The rice farmers in the Niigata prefecture in the hills of Japan searched for many years to find a fish that they could breed in their ponds as a food source during harsh winters if rice production was low.
The farmers of the Niigata prefecture over 500 years ago started to realise that when a group of fish were bred for decades in the same isolated pond that the colour of some individuals will be different over time. This was the beginning to the understanding of recessive and dominant genes. They would place the fish with the different colour into a curtain pond and remove the fish with the former colour. They found that after a period of time this new colour would soon become the new colour of the fish isolated in that same pond.
Once the new colour became very dominant, they would then start cross-breeding the fish from one pond with curtain colours with fish from another pond which had different colours. They then bred these two unique colours together, forming a new colour again that would stabilise over time. Over the last 500 years, hundreds of colours of Koi have been created.
In the early days, the farmers would take these fish to the markets and sell them to wealthy people who enjoyed keeping them as pets. The finest colour would be offered to the emperor for him to enjoy in his pond. Having the emperor accept one of your fish was a huge honour for a peasant farmer from Niigata.
The aim was to create fish with a very balanced, strong colour. The colour was to be balanced from left to right and from front to back. If the colour was unbalanced then the fish would look lopsided in the pond. A fish with good colour and good balanced is a most prized fish, commanding a very high price. The fish which had good colour without balance would be a medium quality fish. A fish without colour or balance is a low quality fish. The colours of these fish are random so breeding well-balanced parents does not guarantee well-balanced colour in the offspring. Breeding high quality parents does improve the chance of high quality offspring.
Today the Japanese Koi industry is worth billions of dollars and the attraction and appreciation of these fish is rapidly growing all around the world. These fish are extremely robust and easy to keep making them suitable for many situations. As with all fish, they will only grow to a certain size within any certain water volume so people that keep them in small aquariums will still get to enjoy these fish but they will remain small. To really appreciate these fish at their best, they need to be housed in a very large outdoor pond equipped with excellent filtration. It is worth taking the extra effort to ensure the right conditions and foods are present for these wonderful fish, as they regularly live 40 years and some have been reported to live over 200 years.
Koi are quite a messy fish capable of growing 10cm per year, so it is important not to overstock your pond or your will not allow them the room to grow to their capacity (about 100cm long). Many people start with a large number of hand-picked Koi for their pond but each year sell off the lower quality fish until they are left with a handful of large specimens worthy of entering a Koi show. Koi shows are a very popular hobby which allows breeders and hobbyists to show off and compare their prized specimens. Koi shows are held regularly in most countries in the world. In a show the female tends to be the most prized as they have a larger more imposing body shape. The males have more of a torpedo shape, smaller and more slender then the solid, fat and chunky females.
In countries like Australia Koi are illegal to import so the industry has to rely on breeders to maintain and grow the varieties already available. In these countries it is illegal to return Koi to a river as they can destroy waterways. Even if you catch the fish you are to destroy it not return it. Koi are prone to many diseases so it is very important that you select a credible supplier. Some of the Koi HIV viruses are incurable and not easy to recognize. A 10 minute salt bath (130gm of salt per 4.5lt) for every new fish that you add to your pond will reduce the risk of many infectious diseases.
Koi will eat a large range of foods but it has been proven that high quality Koi pellets are the cleanest and best way to enhance the colour and health of these fish. Many foods such as bread and vegetables are enjoyed by the fish but do tend to pollute the water and offer the fish very little digestible nutrients. People that aim to grow their fish and create jumbo-sized pets tend to feed their fish several times a day and perform partial water changes several times a week, whereas people that wish to maintain their fish as they are will only feed several times a week. The larger the amount of food you introduce the better the pond and filters must be and the more maintenance you will need to do.
Good luck and enjoy