Butterfly koi is a koi with an elongated fine. other names are longfin koi, high fin koi or dragon carp. This type is koi is a by-product of cross breeding a wild Indonesian high fin carp to domesticated Nishikigoi, their purpose is to strengthen the hardness of the koi. The result of the breeding is a longer fins, barbels and the nostril has pom pom formation just like pompom goldfish. In Japan, they are called Onagoi or Hire Naga goi in English longtail carp. Here is a video below.
Butterfly koi origins conflict
I am bit confused on Wikipedia Butterfly koi and Aquascape site they have different claims on how the butterfly koi was made in Wikipedia they said that it was the Japanese breeders but in Aquascape they said it was the American breeders Blueridge, But for me, Whoever made them I am thankful, because, I enjoy keeping them and watching their beauties in my pond.
This is what Wikipedia says
Butterfly koi originated in the mid-20th century as a result of an effort to increase the hardiness of traditional koi. Japanese breeders interbred wild Indonesian longfin river carp with traditional koi. The resulting fish had longer fins, long barbells, pompom nostrils, and were hardier than koi. These were known in Japan as “onagaoi” or “hire naga goi”, or translated in English “long tail carp”. Randy LeFever, the son of Wyatt LeFever, a noted breeder of koi, is credited with suggesting they looked like butterflies, a trait for which the breed is named. They are also sometimes referred to as Dragon Koi.
For clarification, the word koi is wholly inaccurate for describing these fish; Koi are, as dictated by the Japanese breeders, Nishikigoi, these long-finned carp are Hirenagagoi. The word koi has been given to these fish to increase their resale value and popularity in garden centres and the like.
First, let’s consider where butterfly koi originated. In the early 80s, a population of common, brown and grey carp with long fins were found in a series of canals and ditches in Indonesia. A company in New York took an interest and brought the fish into the U.S. and sold some. They did not sell well because they were ugly. However, an enterprising and curious group of breeders at Blue Ridge Fish Hatchery placed an order for a dozen of these fish to see what the heck they were. Ugly, with long fins, is what they discovered. Over the next several years they bred these large, long finned mutations with their finest regular-fin koi and made several discoveries.