Dating back over two millennia, the koi species and their relatives, the carp, have a history shrouded in speculation. Some references claim that koi are descendents of a black fish called Magoi, and that color mutations did not take place until the 18th or 19th centuries. Koi did not originate in Japan, as is commonly thought, even though today they hold the title as the national fish of Japan. Their name Nishikigoi is a contraction of the Japanese words for colorful and carp.
Some of the oldest Asian and other Far Eastern paintings, carvings, and other artwork depict this colorful fish. The earliest written records of koi have been found in China.
Although often thought of as another form of goldfish, koi differ in their origins and in some physical characteristics. Koi grow larger than goldfish and koi have two pair of barbels (specialized fleshy structures covered with taste buds), while goldfish have none.
Koi-keeping did not become popular until the 20th century, with Japan leading the world in developing new varieties. Some of the most ardent koi-keepers are located in the United States and the United Kingdom.