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.
Banded knifefish
The banded knifefish ("Gymnotus carapo") is a species of gymniform knifefish native to a wide range of freshwater habitats in South America. It is the most widespread species of "Gymnotus", but it has frequently been confused with several relatives, including some found outside its range like the Central America "G. maculosus". The English name "banded knifefish" is sometimes used for the entire genus "Gymnotus" instead of only the species "G. carapo".