The Koi, or Japanese Koi, is a domestic variant of the Amur carp. Generally, these fish have brightly-colored scales with various patternThe Koi, or Japanese Koi, is a domestic variant of the Amur carp. Generally, these fish have brightly-colored scales with various patterns. Many variants and color morphs exist across the globe. Though related, these fish differ from goldfish, as they originate from a different species of carp.s. Many variants and color morphs exist across the globe. Though related, these fish differ from goldfish, as they originate from a different species of carp.