Ozutsu

Tail section. This term is used for the part of the body located from the end of the dorsal fin to the root of the tail. It is an important section because it contains the Odome. In addition, Nishikigoi with thick Ozutsu look powerful, while koi with thin Ozutsu look feeble. If a Koi has a thick Ozutsu while it is young it may have the potential to grow into a Jumbo Koi. Obachi specifies the top section of the Ozutsu, not the sides or the bottom.

(Courtesy of the excellent Book Kokugyo Vol II)