The round goby, <i>Neogobius melanostomus</i> (Pallas, 1811) was introducedinto southern Baltic waters (including the Vistula Lagoon) fromthe Black Sea and Sea of Azov in the early 1990s. This studydescribes the parasites of the round goby in its new environment.In 2004, 486 round goby specimens from the Vistula Lagoon wereexamined for parasites. The following taxa were identified:<i>Dermocystidium</i>sp.; Protozoa: <i>Trichodina domerguei domerguei</i> (Wallengren,1897); Digenea:<i>Cryptocotyle concavum</i> (Creplin, 1825),<i>Diplostomum</i> spp.,<i>Tylodelphys clavata</i> (Nordmann, 1831),<i>Bunodera luciopercae</i> (Müller, 1776);Cestoda:<i>Bothriocephalus scorpii</i> (Müller, 1776),<i>Eubothrium crassum</i> (Bloch, 1779),<i>Paradilepis scolecina</i> (Rudolphi, 1819),<i>Proteocephalus filicollis</i> (Rudolphi, 1802),<i>P. gobiorum</i> Dogel et Bychovsky, 1939,<i>Proteocephalus</i> sp.;Nematoda:<i>Anguillicola crassus</i> Kuwahara, Niimi et Itagaki, 1974,<i>Camallanus truncatus</i> (Rudolphi, 1814),<i>Contracaecum</i> spp.,<i>Cystidicoloides ephemeridarum</i> (Linstow, 1872),<i>Dichelyne minutus</i> (Rudolphi, 1819),<i>Hysterothylacium aduncum</i> (Rudolphi, 1802);Acanthocephala:<i>Echinorhynchus gadi</i> Müller, 1776,<i>Pomphorhynchus laevis</i> (Müller, 1776).The parasites found were all local species, already reported fromPoland. Except for <i>Dermocystidium</i> sp., <i>C. concavum</i>,<i>P. gobiorum</i>, and <i>D. minutes</i>, they have already been recorded inother fish species in the Vistula Lagoon. The prevalence andmean intensity of infection was low (18.3%; 4.0 indiv. - thisvalue does not include ciliates). The most frequent parasitesincluded <i>H. aduncum</i> (9.9%, 1.2 indiv.) and <i>A. crassus</i> (9.1%,1.2 indiv.). In addition, <i>Dermocystidium</i> sp., <i>B. luciopercae</i>,<i>E. crassum</i>, <i>P. scolecina</i>, <i>P. filicollis</i>, <i>C. truncatus</i> and <i>C. ephemeridarum</i> are reported from the round goby for the first time. As the fishhas only recently appeared in the Vistula Lagoon, its parasitic fauna has not yet developed to the full
