This is the jewel of the Japanese goldfish and it is one of my favorites but very hard to find. You have to pay a very high premium to get a mature fish. These fish was almost come to extinction but someone in Japan had revived this species when he found a few pieces down in a ruin restaurant basement just after WWII.
Its main characteristic is on it tail which is wedged or fused together not like the other goldfish. Its ruffled tail should wrap towards its haed and the front end tips of the tail are curving down and up at the very tip. It should also have a upright dorsal fin.