Koi
The major named varieties include:Goldfish (金魚) were developed in China more than a thousand years ago by selectively breeding Prussian carp for color mutations. By the Song dynasty (960–1279), yellow, orange, white, and red-and-white colorations had been developed. Goldfish ("Carassius auratus") and Prussian carp ("Carassius gibelio") are now considered different species. Goldfish were introduced to Japan in the 16th century and to Europe in the 17th century. Koi, though, were developed from common carp in Japan in the 1820s. Koi are domesticated common carp ("Cyprinus carpio") that are selected or culled for color; they are not a different species, but a subspecies, and will revert to the original coloration within a few generations if allowed to breed freely.
Asian carp in North America
The common carp was brought to the U.S. in 1831 and has been widespread for a long time. In the late 19th century, it was distributed widely throughout the United States by the United States Fish Commission as a foodfish. However, common carp are not now normally prized as a foodfish in the United States. They are often known to uproot vegetation and muddy water through their habit of rooting in the mud for food. They are thought often to have detrimental effects on native species. However, in Europe, common carp are prized as a sportfish, and angling for common carp is enjoying increased popularity in the United States.