Abstract
The Shortfin Molly, Poecilia mexicana, is herein reported for the first time from Japan on the basis of specimens collected from the Nitanda River (hot spring water) in Ibusuki City, Kagoshima Prefecture. The fish from Ibusuki City, previously misidentified as P. sphenops, is believed to represent an introduced population from the west coast of Central America (original locality of the species) or other places. Poecilia mexicana is characterized by having 9 dorsal- and anal-fin soft rays, 18 caudal-peduncle scales, unicuspid upper-jaw inner teeth, sensory pores on the dorsal surface of the snout, and the broad vertical orange band on the caudal fin in mature males. Morphological changes with growth and sexual dimorphism of Japanese P. mexicana are also described. A new Japanese name “Surikogi-mori” is proposed for the species.
