Natural History of Musashino Minamisawa (III)

Intermediate-Type at the Coexistence (Ochiai River) of two Species of genus Phoxinus

Abstract

Two species of the genus Phoxinus, P. lagowskii and P. oxycephalus are distinct species that can be distinguished by morphology and distribution, but juveniles are difficult to identify by morphology. We documented the growth process of Phoxinus from juveniles and examined the length at which it became distinguishable, and conducted subsequent surveys. We conducted RFLP analysis of mitochondrial cytochrome-b and morphological analysis of the appearance of 275 individuals of Phoxinus sp. collected from four rivers including the Ochiai River in Higashikurume City, Tokyo, where both species are considered to coexist. In the Ochiai River, we found hybrids between P. lagowskii and P. oxycephalus, and that both species have been present for many years. The distribution of these fishes in the Ochiai River suggested that there may be areas in the Ochiai River where both species can coexist and areas where hybrids of both species are formed.