Koi, or more specifically nishikigoi, literally ("brocaded carp"), are ornamental domesticated varieties of the common carp (Cyprinus carpio) that are commonly kept for decorative purposes in outdoor ponds and water gardens. They are sometimes also called Japanese carp.
Koi were developed from common carp in Japan in the 1820s, and are still very popular there as they are a symbol of love and friendship. Many different colors and color patterns and have since been developed; common colors include white, black, red, yellow, blue, and cream. The most popular category of koi is the Gosanke, which is made up of the Kohaku, Taisho Sanshoku, and Showa Sanshoku varieties.