Morphological and Taxonomical Studies on Natural Hybrids of the Pufferfih Genus Takifugu.

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Materials for this research were collected from the Japan Sea coasts of Honshu and from the west coast of Kyushu. Morphological examinations on these materials revealed that there are three natural hybrids in the genus Takifugu; they are (I) Takifugu xanthopterus x T. rubripes, (II) T. xanthopterus x T. vermicularis, and (III) T. porpbyreus x T. rubripes (or T. chinensis). The hybrid (I) is characterized by having small spines on the dorsal and ventral sides of the body, black back with oblique patterns of white lines and spots. This hybrid has been collected from the waters around Kyushu. The hybrid of (II) shows intermediate conditions between T. xanthopterus and T. vermicularis in the body shape and color. It is distinct in the combination of the following characters: all fins yellow, dorsal side of body dark brown with many irregular white spots, and weak minute spines on the dorsal and ventral sides of the body. This hybrid has been collected in Ariake Bay. The hybrid of (III) is characterized by having very weak spines on the dorsal and ventral sides of the body, black back of the body with a large round black blotch on the side behind the pectoral fin, and the white anal fin. This hybrid has been known from the East China Sea and the western part of the Japan Sea.The nomenclatural confusion about the generic name of Takifugu was carefully clarified. Literature surveys revealed that Fugu, which has been frequently used by many authors, is actually a junior subjective synonym of Takifugu.Japanese species of Takifugu were also examined to clarify their systematic features. A key to these species was given.