Parasite fauna of the eel, Anguilla anguilla [Linnaeus, 1758], from the Polish part of the Vistula Lagoon

Introduction. Eel is one of the most valuable commercial fish species of the Vistula Lagoon. For this reason its infection by non-indigenous species of parasites is the subject of the interest of sciencists. Material and methods. A total of 90 eel specimens caught in the Polish part of the Vistula Lagoon were examined over the period of May-August 2005. The fish were subjected to standard procedures of parasitological examination and parasite identification. The fish were divided into two length classes: smaller and larger than 50 cm. To assess the effects of parasites on fish condition, the Fulton coefficient, expressed with the formula: WF = G · L⁻³ x 100, was calculated. Results. The fish were found to be hosts to 17 parasite taxa. The Ciliophora were represented by Trichodinella epizootica (Raabe, 1950); the Myxozoa by Myxidium giardi Cépede, 1906; the Digenea by Bunodera luciopercae (Müller, 1784), Deropristis inflata (Molin, 1859), Diplostomum spp., and Ichthyocotylurus platycephalus (Creplin, 1852); the Cestoda by Bothriocephalus claviceps (Goeze, 1782), Proteocephalus macrocephalus (Creplin, 1815), and Proteocephalus sp.; the Nematoda by Anguillicola crassus Kuwahara, Niimi et Itagaki, 1974, Camallanus lacustris (Zoega, 1776), C. truncatus (Rudolphi, 1814), and Hysterothylacium aduncum (Rudolphi, 1802); the Acanthocephala by Acanthocephalus lucii (Müller, 1776) and Corynosoma strumosum (Rudolphi, 1802); the Hirudinea by Piscicola geometra (Linnaeus, 1761); and the Copepoda by Ergasilus sieboldi Nordmann, 1832. All fishes were infected, and the mean intensity of all parasites was 4.8 inds. The nematode Anguillicola crassus was the most frequent parasite (67.8%, 4.2 inds), represented by all developmental stages, but mostly by adult specimens. The fish condition coefficient was somewhat higher in the eel larger than 50 cm (0.1746) than in those smaller than 50 cm (0.1734); in addition, only Anguillicola crassus-free fish showed a higher condition coefficient (0.1861), compared to the infected specimens (0.1715).