Tosakin

The Tosakin, sometimes called the Curly Fantail or Queen of Goldfish, is a rare and highly distinctive breed native to Kochi Prefecture (formerly Tosa Province) in Japan, where it has been designated a natural monument. Its most extraordinary feature is the enormous tail fin that, while technically divided, fuses at the center to form a single horizontally spreading fin that curves and ruffles near the water's surface. This unique tail is best appreciated from directly above, and Tosakin are traditionally kept in shallow round basins specifically for top-view observation. The fins are extremely delicate and will deform in even mild water currents, so tanks must have minimal or no filtration flow. Tosakin are gentle in temperament but should always be kept separately from other species to protect their fragile fins. Breeding and maintaining the characteristic tail shape requires considerable expertise, making Tosakin one of the most challenging and rewarding goldfish varieties for advanced hobbyists.

Source: Wikipedia (CC BY-SA 4.0)

Goldfish pellets (small amounts, multiple times)