The present study was to investigate the copepodid species infecting rosy goatfishParupeneus rubescens,one of the most economically important fishes in the Arabian Gulf. A copepodid species identified from the examined fish specimens belongs to the Taeniacanthidae family and is labeled as Taeniacanthus yamagutii Shiino, 1957, mainly depending on its morphological, mor-phometric, and ultrastructural characteristics, in particular the presence of maxilliped claw with a conspicuous digitiform process at the base, the terminal process of the second maxilla stout, and a setiform element at the tip of each exopod spine of legs 2–4. In order to ensure the accurate identification and exact taxonomic characterization of this species, the28S rRNA gene sequence was analyzed. The result revealed that the presentcopepodid species belong to the Taenicanthidae family and has a close relationship with Taeniacanthus yamagutii (gb| KR048852.1) in the same taxon. The present study demonstrated that the rosy goatfishis a host for Taeniacanthus species, which will be helpful to prevent this parasitic infection.