The Japanese bred koi fish for perfection with distinctive colours and patterns and some species were even prized in the collections of royal families and immortalized in royal artworks. It was not until the 1900s that koi began to be bred in parts of Europe and the United States.
Koi fish are quite large and, with proper care, can grow to be between two and three feet in length. The Chagoi variety of koi get even larger and may grow to four feet long. Young koi can be kept in large indoor aquariums but need to be transferred to a large pond as they grow. They are a heavy-bodied fish with an average weight of around 35 pounds