First record of Pontian Monkey Goby, Neogobius fluviatilis (Pallas, 1814) in the Evros River (Greece); Is it an alien species?

The Pontian Monkey Goby, Neogobius fluviatilis (Pallas, 1814), was recorded for the first time in Greece in August 2011. Eight specimens were collected in the Greek-Turkish section of the Evros River, 65 kilometers upstream of its river-mouth. Although the species has been recently discovered in the Tundza, a tributary of the Evros in Bulgaria, it has never before been found in the Evros’ main stem.  Although the lower Evros has been poorly researched by ichthyologists, it is unlikely that a conspicuous medium-sized fish would go unnoticed in this river; and, it is therefore suggested to be a probable alien. However, since the Evros basin has had geological connections to the Marmara Sea and Black Sea in the past and it is immediately adjacent to native populations of N. fluviatilis , the species status is categorized as questionable until genetic and morphological studies are completed.