Proterorhinus semipellucidus is a species of gobiid fish, a tubenose goby originally described from the Gharasu River near Gorgan Bay of the Caspian Sea in Iran. Following the systematic decomposition of the tubenose gobies it was suggested to be a more widespread and invasive taxon distributed in the fresh waters of the Caspian Sea basin. It may be the same species as that known as Proterorhinus nasalis.