Hirenaga 鰭長
Hire鰭 means dorsal fins, naga長 means long. Hirenaga Nishikigoi refers to Nishikigoi with long fins.
Hirenaga Nishikigoi was produced by Saitama Fisheries Research Institute. In 1977, the reigning Emperor (the Crown Prince at that time) visited there and advised to mate Hirenaga-koi in Indonesia with Japanese Nishikigoi to create the new elegant variety. They started to crossbreed and fixed it as one variety named “Hirenaga Nishikigoi” in 1982. You can keep them just by following the same ways as Nishikigoi.
Pictures of Hirenaga bred by Kurihara Koi Farm in Saitama, Saitama is the birthplace of Hirenaga Nishikigoi.
Article on Hirenaga
