Three scales generally refer to mirror carp, which is a variety of European carp. Its skin is shiny, as smooth as a mirror and its luster is obvious, so it is called mirror carp. Under reasonable stocking density and better feeding conditions, mirror carp grows very fast.

Mirror carp originated in Europe, and was introduced from West Germany by China. After more than 20 years of systematic breeding by Heilongjiang Fisheries Research Institute, a German mirror carp breeding line suitable for breeding in most parts of China has been selected. The most remarkable feature of the selected line is that it is greatly improved in cold resistance and disease resistance compared with the original seed.