Several specimens of Cynoscion regalis have been captured in the Sado Estuary, western Portugal. This species is a common inhabitant of the shallow marine and oligohaline waters of eastern North America. Evidence of this species just 5,000 km to the east of Portugal is surprising, but identification has been confirmed by morphometric characters and the CO1 gene sequence. This recent discovery could be due to ship transport: the main pathway for alien marine fish invasions.