Goldfish, as a result of having gills, require oxygen in order to survive. Encyclopædia Britannica references that all fish have gills, which are used to exchange oxygen and carbon dioxide with the surrounding water. Goldfish are members of the carp family, and lived in ponds in Asia before domestication.
Goldfish were domesticated before or during the Sung dynasty, which ran from 960 to 1279. They have a naturally greenish-brown or gray color, although selective breeding has produced many colors, such as black, golden and white. Goldfish are omnivorous, eating a variety of plants and small animals. During spawning season in spring or summer, the goldfish's color becomes brighter.