Natural History of Musashino Minamisawa (IV)

Origin of Hybrids of the Genus Phoxinus in the Ochiai River and Changes in the Ecosystem by Domestic Invasive Fishes

Abstract

The Kanto region was previously inhabited only by Phoxinus lagowskii. However, we have already observed P. oxycephalus-like fishes and individuals that appear to be hybrids of both species in the Ochiai River in Tokyo, suggesting the possibility of an invasion of P. oxycephalus. In this study, we analyzed maternally inherited mitochondrial cytochrome-b RFLPs and external morphology using 154 individuals collected from the Ochiai, Yokose, and Nariki rivers in the Kanto region, four rivers in Okayama Prefecture where P. oxycephalus are dominant, and two rivers in Mie and Nara prefectures, which are at the distributional boundary of the two species. The results showed the possibility of gene transfer from the distribution boundary area to the Ochiai River. Hybridization and coexistence of the two species were also observed in other rivers. The fact that the introduction of domestic invasive species has been observed in many rivers indicates the possibility of accidental and anthropogenic migration by releasing juvenile fish, and the disturbance of the ecosystem by domestic invasive species may be occurring in each river.