The fine structures of mature spermatozoa of 13 Japanese osmerid and salmonid species (and subspecies) were studied with TEM and SEM. Three types were recognized, based on combinations of morphological characters, such as nucleus shape, number, size and arrangement of mitochondria, and numbers of flagella, as follows: Osmeridae type (7 species, including Osmerus eperlanus mordax, Hypomesus nipponensis, Hypomesus japonicus, Spirinchus lanceolatus, Mallotus villosus, Plecoglossus altivelis altivelis and Plecoglossu altivelis ryukyuensis), characterized by an elongated ovoid nucleus with a deep cylindrical basal fossa, a single mitochondrion, located along the base of the flagellum, and a single finned flagellum; Salangidae type (4 species, including Salangichthys microdon, Salangichthys ishikawae, Salanx ariakensis and Neosalanx reganius), characterized by a spherical nucleus with a partly invaginated, moderately deep conical basal fossa, multiple mitochondria surrounding the flagellum; and a single finned flagellum; Salmonidae type (2 species, including Oncorhynchus masou masou and Oncorhynchus mykiss) being characterized by a depressed ovoid nucleus with a shallow cylindrical basal fossa, a single mitochondrion, annular around the base of the flagellum; and a single finned flagellum. A comparison between these types and currently-recognized osmerid and salmonid systematics revealed the following: (1) The Osmeridae type variously included Hypomesinae, Osmerini (Osmerinae) and Precoglossinae sperm morphs; (2) the present grouping of sperm morphs is less supportive of some recently proposed systematics of relevant taxa, although concurring with a recent molecular phylogenetic study. It is suggested that spermatozoa are potentially useful in evaluating generic relationships within Osmeridae.
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