Abstract
In 1993 and 1999, a number of specimens of a poecilid fish collected from a drainage area of the hot spring at Kojyohama, Shiraoi-cho, Shiraoi-gun, southern Hokkaido, Japan was identified as Poecilia sphenops. Identifications were based on males having elongated pelvic-fin tips, in having the dorsal-fin origin posterior to a vertical through the pelvic-fin base, 9-10 dorsal fin rays, no horizontal pigment band and ocellus on the body, no opening of the cephalic sensory canal on the snout, and many tricuspid teeth in the inner row of teeth on the upper jaw. It is believed that small fish were introduced into this area longer than 20 years ago to assist in reducing mosquito populations. At present, high density schools of these small fish were observed swimming throughout the drainages. This report represents the record of habitation and natural breeding of this species in Japan.
