Systematic revision of southeastern asiatic cyprinid fish genus Osteochilus with description of two new species and a new subspecies

Abstract

                      The cyprinid fish genus Osteochilus is revised using data obtained from meristic counts. morphometric measurements, and an osteological analysis. Some cladistic techniques were used in erecting a phylogeny but the evolutionary approach was employed in translating the phylogenetic information into a classification. In those species for which specimens were not available (none of which are valid species of Osteochilus), data from the literature were carefully evaluated. Fifty-one nominal species have been assined to Osteochilus at one time or another of which 16 species are removed from the genus and three others are of uncertain status and are only provisionally retained in Osteochilus. Twenty-one valid species are redescribed. Two new species and one new subspecies are described, making 23 species of Osteochilus recognized in this study.

                        Osteochilus is probably derived from a Labeo-like ancestor, since the two genera share many common characteristics. The distinguishing features of the genera are regarded as specializations from the more generalizd condition in the subfamily. With our present knowledge it is difficult to say which genus, Labeo of Osteochilus,  is the more primitive.

                       The center of origin, evolution, and radiation of Osteochilus was  examined on the basis of the specimens studied and from the literature. The center of abundance of Osteochilus species is in the western Borneo and southernSumatra area, where there are 13 and 12 species, respectively. The occurrence of the same species on the mainland of Southeast Asia and on the islands of Sumatra,Borneo, and Java is probably explained by the fact that these land masses were once connected during the Pleistocene when the sea level dropped by 100 metres. Some species are unevenly distributed which indicates either that some species have been extirpated regionally because of unfavorable factors, that they arose after the land masses were separated, or the more extensive field collecting activities are needed in order to reveal a more cohesive pattern of distribution. Regrettably, it is still impossible to pinpoint a subregion of southeasternAsia as the center of oringin for the genus.