Ophiotaenia europaea Odening, 1963 (Cestoda: Onchoproteocephalidea) adopts a North American brown bullhead catfish Ameiurus nebulosus Lesueur, 1819 as intermediate/paratenic host in Europe.
Natural infection of non-native brown bullhead catfish Ameiurus nebulosus Lesueur, 1819 (Siluriformes: Ictaluridae) with larvae of the cestode parasite Ophiotaenia europaea Odening, 1963 (Onchoproteocephalidea) was confirmed at several localities in the Czech Republic, this representing the first record of O. europaea larvae in the country. Adult cestodes infect the intestinal tract of colubrid snakes [predominantly grass snakes Natrix natrix (Linnaeus, 1758) and dice snakes Natrix tessellata (Laurenti, 1768)], with cyclopoid copepods and fish and/or frogs as the first and second intermediate hosts, respectively. Brown bullhead was introduced to Europe from North America during the last century and has since become widely distributed in many European countries. Larval cestodes were found encysted in the brown bullhead mesentery and on the surface of the intestine and kidney; all parasites were alive. Species identification was confirmed using sequencing of partial 18S and 28S rDNA and COX1 mtDNA. Brown bullhead are only the second natural intermediate/paratenic host of O. europaea reported, and the first confirmed by molecular genetics. Its wide distribution within different populations of A. nebulosus indicates that this non-native fish species has been successfully included into the life cycle of O. europaea. Dice snakes, one of the two natural definitive hosts of O. europaea, are rare in the Czech Republic and classified as an endangered species; and larvae of O. europaea were predominantly found in localities close to the distribution area of this snake species. Possible impacts of bullhead catfish introduction into regions with dice snakes are discussed further.