Koi (鯉, English: /ˈkɔɪ/, Japanese: [koꜜi]) or more specifically nishikigoi (錦鯉, [ɲiɕi̥kiꜜɡoi], literally “brocaded carp”), are colored varieties of Amur carp (Cyprinus rubrofuscus) that are kept for decorative purposes in outdoor koi ponds or water gardens.

Koi is an informal group of the colored variants of C. carpio. Several varieties are recognized by the Japanese. Koi varieties are distinguished by coloration, patterning, and scalation. Some of the major colors are white, black, red, orange, 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.

1 Koi Kohaku
2 Koi Taisho Sanke (Sanke)
3 Koi Showa Sanshoku (Showa)
4 Koi Utsuri
5 Koi Bekko
6 Koi Asagi
7 Koi Shusui
8 Koi Tancho
9 Koi Goromo
10 Koi Kin/Ginrin
11 Koi Goshiki
12 Koi Hikarimuji
13 Koi Hikarimoyo
14 Koi Hikari Utsuri
15 Koi Kawarimono
16 Koi Doitsu koi
17 Koi Yamato Nishiki
18 Koi Kanoko koi