The word 'Koi' comes from Japan, but Koi fish originated from China. The koi word means carp, the exact term is the Cyprinus carpio. You probably heard that word: Nishikigoi, this is a more specific term for colorful carp.
Koi has a lot of color varieties and they are related to goldfish. Koi caring and breeding is very simple.

Koi keeping become popular in the 19th century. Farmers working the rice fields noticed that some colored carp, captured them, and raised them. By the 20th century, a number of color patterns had been established. Niigata Koi were exhibited in an exposition in Tokyo in 1914. After that the hobby of keeping Koi spread worldwide. Koi are now commonly sold in most of the pet stores.

You can differentiate the varieties by color and pattern. Koi pond have many different colors: white, black, red, yellow, blue, and cream. The variations are limitless, breeders determined different categories. The most popular category is Gosanke.

Some example from the koi varietis:

Kohaku: a white-skinned Koi, with a red pattern
Taisho Sanshoku (Sanke): a white-skinned Koi with a red and black pattern
Showa Sanshoku (Showa): a black-skinned Koi with a red and white pattern
Bekko: a white, red, or yellow-skinned Koi with a black pattern
Ghost koi: "Hybrid" of Ogon and wild carp. Not Nishikigoi.
Butterfly koi: Long-finned version of all others. Not Nishikigoi.

Kois live in the wild in every continent except Antarctica. Some places in the world Koi keeping is illegal, and some other places people tried to eradicate them. Koi increase the turbidity of the water and it can cause damage to the environment.

This beautiful fish has place in the world and a lot of people has passion for these ponds.