Carassius auratus is a freshwater fish in the family Cyprinidae of order Cypriniformes. It was one of the earliest fish to be domesticated, and is one of the most commonly kept aquarium fish. It was first domesticated in China more than a thousand years ago, and several distinct breeds have since been developed, varying greatly in size, body shape, fin configuration and colouration: various combinations of white, yellow, orange, red, brown, and black are known.
By the time of the Song dynasty (960–1279), the domestication of goldfish was firmly established. In 1162, the empress of the Song Dynasty ordered the construction of a pond to collect the red and gold variety. People outside the imperial family were forbidden to keep goldfish of the gold (yellow) variety, yellow being the imperial colour. This is probably the reason why there are more orange goldfish than yellow goldfish, even though the latter are genetically easier to breed. The occurrence of other colours was first recorded in 1276. In 1603, goldfish were introduced to Japan, and In 1611, to Portugal, and from there to other parts of Europe. Goldfish were first introduced to North America around 1850, and quickly became popular in the United States.