Tosakin

The Tosakin (土佐金) or curly fantail goldfish is a distinctive breed of goldfish with a large tail fin that spreads out horizontally (like a fan) behind the fish. Though technically a divided tail, the two halves are attached at the center, forming a single fin.

It was developed in Japan, and is rarely seen in other countries. It is believed to have originally been developed from the ryukins and Osaka ranchus.