First reliable Japanese record of Richardsonichthys leucogaster (Tetrarogidae) from Amami-oshima Island, Ryukyu Islands, Japan

Abstract

A single specimen of Richardsonichthys leucogaster (Richardson, 1848) (Tetrarogidae) from the Oshima Channel (between Kakeroma-jima and Amami-oshima Islands), Ryukyu Islands represents the first reliable record of the species from Japan, the species having been previously recorded from Taiwan, the northernmost northwestern Pacific Ocean record. Although previous literature has included Japan in the distribution range of the species, no reliable specimen-based records have been reported. The present specimen (a small juvenile, 17.1 mm standard length) possessed the following features, characteristic of the monotypic genus Richardsonichthys Smith, 1958: body completely naked, except for lateral-line scales; head profile rounded; dorsal fin with 13 spines and 8 soft rays; dorsal fin origin anterior to posterior margin of orbit; membranes of spinous dorsal fin not divided (anterior 3 spines not separated from subsequent spines); anal fin with 3 spines; pelvic fin with 5 soft rays; and eye surface with 4 short tentacles. The specimen also had mostly black pelvic and anal fins, probably characteristic juvenile coloration. The new standard name “Umanohoshi-haokoze” is proposed for the species.