The koi is a decorative variety of the common carp, or Cyprinus carpio, which is bred and kept for ornamental purposes in outdoor ponds and water gardens. It was first bred for various color patterns in Japan in the 1820s. The word "koi" is the general Japanese word for carp and the word "nishikigoi" is used when specifically referring to the multicolored carp.
While most koi do not reach the exceedingly long life span sometimes attributed to the species, the oldest koi fish lived to be 226 years old. This fish, named Hanako, died on July 7, 1977, according to Mother Nature Network. Some estimate the age of the fish by counting the rings on its scales known as annuli. Koi typically grow to reach 2 to 3 feet long and weigh approximately 35 pounds. They are a species of common carp fish bred through the centuries by Japanese rice farmers to have the color variations they are known for today.Learn more about Fish