They are ornamental varieties of domesticated common carp (Cyprinus carpio) that are kept for decorative purposes in outdoor koi ponds or water gardens.
Brocated Koi varieties are distinguished by coloration, patterning, and scalation.
Some of the major colors are white, black, red, yellow, blue, and cream.
The most popular category of koi is the Gosanke, which is made up of three varieties, Kohaku(red&white), Showa-Sanshoku(red&black patterns on white) and Taisho-Sanshoku(red and white patterns on black).
A fry carp is not expensive, but once they grow up to be a large beautiful Koi, it may be traded for over U.S.$100,000.
There is a rumor that some Kois increase 1000% in value over a year.
Photo by Guillaume Nargeot