Intestinal nematodes of the Aythyini ducks in Western Pomerania. Biology, including ecology, of the Aythyini renders them particularly attractive subjects of parasitological studies. The tribe is represented in Poland by 4 nesting species; two of them, Aythya fuligula and A. ferina, are very abundant game birds. However, their helminth fauna, including nematodes, is still very poorly known. This study was aimed at quantifying the structure of parasitic intestinal nematodes of the Western Pomeranian Aythyini. The study, performed in 1999-2004, involved a total of 71 ducks representing 3 species: A. ferina, A. fuligula, and A. marila. The nematodes, isolated from the intestines, were fixed in 75% ethyl alcohol and cleared in lactic acid. Among the 9668 helminth individuals found, 589 (6.1%) represented the phylum Nematoda. They were found in 57 ducks (80.3% of all the ducks examined). The nematodes belonged to the following 4 families: Amidostomatidae, Tetrameridae, Acuariidae, and Trichuridae. They were identified as representing 8 species, 2 genera (Amidostomoides sp. and Tetrameres sp.), and 1 subfamily (Capillariinae gen. sp.); in addition, 1 damaged individual could be identified as a nematode only. The highest prevalence (57.8%), at mean intensity (4.8 inds), was typical of Amidostomoides petrovi (Shakhtahtinskaya, 1956) Lomakin, 1991, while Tetrameres fissispina (Diesing, 1861) Travassos, 1914 occurred with the highest intensity (15.1 inds) and 12.7% prevalence. Nematodes of the subfamily Capillariinae occurred with a fairly high intensity (averaging 10.0 inds) as well, although their prevalence was not high, either (4.2% of all ducks were infected). The nematofauna studied was clearly dominated by A. petrovi, T. fissispina, and Capillaria anatis (Schrank, 1790). The total frequency of occurrence of those species was close to 80%; their dominance indices exceeded the threshold value of 0.1 and amounted to 1.6 (the dominant A. petrovi), 0.2, and 0.5 (the subdominants T. fissispina and C. anatis, respectively). The three species listed occurred with the highest mean density (2.8; 1.9; and 1.8 nematode per duck examined). No age- (adult vs. immature) or sex- (males vs. females) related differences in the quantitative structure of the parasitic Aythyini nematodes were observed.