Discovery of fossil Ayu (Plecoglossus altivelis) from the Upper Miocene of Shimane Prefecture, Japan

Abstract

The Ayu, Plecoglossus altivelis, comprising three subspecies, is the only species in the genus Plecoglossus in the family Osmeridae. Here, we describe for the first time the discovery of fossil specimens of P. altivelis from the Upper Miocene sediment of Matsue, Shimane Prefecture, Japan. The fossil individuals are subadult and have comb teeth in the second and third generations. These fossil specimens are clearly similar to the recent P. altivelis, the former's meristic characters being included in the three recent subspecies. In terms of numbers of pectoral fin rays and vertebrae, the fossil specimens are more similar to the subspecies Plecoglossus altivelis ryukyuensis than the other subspecies, but they also show different dorsal fin shapes and anal fin ray counts. This discovery of fossil P. altivelis indicates the persistence of the species for at least 10 million years, from the Late Miocene to the present.