Doitsu lineage does not mean Nishikigoi bred in Germany, but rather those Crossbred with Japanese Koi and black carp imported originally for food from Germany. They differ from ordinary Nishikigoi (or "'Wagoi' meaning Japanese Koi) in scale arrangement.

Doitsu Koi with lines of scales on the back and along the lateral lines are called "Kagami-goi (mirror carp)," and those without scales or with only one line of scales on each side along the base of the dorsal fin, "Kawas-goi (leather carp?)."

Doitsu Koi are crossbred into almost all varieties of Nishikigoi. Doitsu Koi are to be viewed for the orderliness of scale arrangement and the absence of unnecessary scales. Each Koi should have the features characteristic of its own original variety, of course.