Rather than having the long slender body of the Common Goldfish or the Shubunkins, the Fantail, or Ryukin as it is known by the Japanese, is one of the more rounded or egg-shaped fancy gold fish.
These fish are bred for showing and its main feature, the split tail fin is medium in length and slightly forked. To be a good show specimen, the tail fin needs to be completely split with the two lobes being much closer together on top than on the bottom, making it look triangular when viewed from the back. Good show specimens also have a double anal fin with complete separation. Those whose tail fins are not completely split won't win any prizes, but still make great pets.
The can grow a little bigger than some fancy goldfish, 6" - 10", and are one of the most hardy varieties of goldfish, tolerating temperatures only a few degrees above freezing, as long as the cooling drops by only a few degrees a day.
When kept in an aquarium they like warmer temperatures, 65°F - 72°F. Again, sinking food is best, as gulping air when trying to eat floating flake food can upset their balance. This can cause them to float upside down until they manage to get rid of the trapped air in their stomach