Data on the presence and distribution of alien species recorded by expert observers in the framework of the project "Presence and health aspects of alien fish species in the western Ionian Sea, eastern Sicily" (year 2019) carried out by the MareCamp association as thesis coordinator for students of the University of Messina. The project included surveys from Catania to Siracusa waters during fishing trips using different fishing gears (trammel, trowler, single net), observation, measurement, necroscopy, microscope analisys, and interviews with fishermen.