The goldfish, or Carassius auratus auratus, is a species of domesticated freshwater fish that belongs to the carp family. These generally hardy fish are best known for their characteristic orange-gold hue, but actually come in a variety of colors and patterns. They also vary in general appearance, some having telescopic eyes, others bubbled; some may have short, simple tail fins, while others may have long, flowing fins that look like veils. These fish are a very popular choice for home aquariums due to their ease of care and friendly demeanor.
Although goldfish may vary in appearance, most are anatomically similar. Goldfish bear numerous fins all across their bodies that help propel, steer, and keep them stable in the water. These fins consist of the tail fin, as well as the dorsal, pectoral, anal, and pelvic fins. The gills, mouth, and eyes are associated with breathing and senses; in some varieties, as with bubble or celestial eyes, visual acuity may be limited. These freshwater fish also bear lateral lines to further help with movement, and what is known as a wen — skin folds that develop on top of the head of some breeds.
The common goldfish, as its name implies, is one of the best-known varieties. Depending upon the environment, this type of fish can grow to anywhere between 4 inches (10.1 cm) and 1 foot (30.4cm), and may be the traditional orange-gold color, as well as white, red, or black. Black moor, fantail, and comet types are also quite popular due to their conspicuous tail fins, which many find to be an attractive variation. Other breeds, such as the pearlscale and panda moor, are less common, and bear unique markings and body shapes.
The goldfish is said to be a direct descendant of the Prussian carp, which comes in colors from olive-brown to a deep silver hue. During China's Jin Dynasty (265-420), a natural mutation rendered the otherwise drab fish into brilliant hues of orange, red, and yellow. During the later Tang Dynasty (618-907), it had become increasingly popular to keep carp as a feature within ornamental ponds, and because of the unusual colors that the mutation produced, this particular species of carp became very stylish to raise and keep. These fish then moved through Japan around 1502, then to Europe, and by 1850 became one of the most popular household pets in the United States.