Aka Japanese Colored Carp, koi are just carp with a genetic color variation. They can get up to 3 feet long and live well over 100 years. Koi first appeared in Japan a couple thousand years ago, I think. They are ornamental fish that do not occur in the wild and are kept as pets in fish ponds. Like dogs, there are established breeds of koi, people have koi shows, and top notch koi in an established genetic line can sell for as much as $15,000. Koi are not goldfish. They can have the colors black, blue, white, yellow, orange, red, brown, and any of these can be metallic. Like their wild cousins, koi are schooling fish and don't have much of a social organization like cichlids do. They can be taught to eat out of your hand (and get big enough to suck on several of your fingers at once), and actually recognize their owners to a certain extent.