Topographic specificity of Diplozoon paradoxum Nordmann, 1832 [Monogenea: Diplozoidae] in the bream, Abramis brama [Linnaeus, 1758] in the Vistula Lagoon, Poland

Location of the monogenean Diplozoon paradoxum on the branchial arches of the Vistula Lagoon bream is described. The highest number of parasites was found on the first gill arch, followed by the numbers recorded on the second and third arches; the lowest numbers of the monogenean were typical of the fourth arch. About 70% of the monogeneas were found to dwell on the dorsal part of the branchial arch. It is concluded that the distribution of parasites is controlled by the direction of water flow through the gills as well as the size of the gill arch occupied by the helminths.