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.
Common goldfish
"Fungal Infection" is the growth of fungus which could lead to problems regarding parasitic infections, ulcers, or open wounds; the fungus symptoms could worsen and lead to a secondary fungal infection. There are “cotton-like growths along the body and fins” which is caused by dirty water. Treatments start from moving the goldfish to a hospital tank and then clearing the environment with Methylene Blue if the condition is serious, however, the goldfish can just have a cleaner tank and the fungal infection should clear up over time.