It is a general term for a class of ornamental fish species that have been artificially improved. They are relatively large, with a body length of up to 0.6-1.5 meters [2] [21], and weigh 10-45 kilograms. The scales come in various colors and types, including whole scales, few scales, and no scales. Body color is influenced by pigment cells and can present rich color changes. Therefore, it is known as the "king of ornamental fish" and is also referred to as the "living gem" and "art piece that can swim". Originating from China, its ancestor is the red carp, which is native to China. Later introduced to Japan, after years of crossbreeding and breeding, the distinctive red carp was formed, which was renamed as koi after World War II.