The goosander, Mergus merganser, is a rare in Poland water bird (Anseriformes: Mergini). It eats fish and small invertebrates. The purpose of this study was a preliminary parasitological examination of the digestive tract of the goosander wintering on the Szczecin Lagoon. The research material were the parasites recovered from digestive tracts of 6 birds (two males and four females), which died during feeding in fishing nets in winter 2001. The birds were subject to standard parasitological examinations using commonly adopted methods. The trematodes and the cestodes found were preserved in 70% ethyl alcohol and subsequently stained using iron carmine (Cestoda) and borax alcohol carmine (Digenea) and then they were closed in Canada balsam. Nematodes were kept in 70% alcohol and cleared with 80% lactic acid or lactophenol. The parasite assemblages were analysed through calculating prevalence, intensity of infection, relative density and domination index. Also, the topic structure of the parasite assemblages or their habitat preferences in a host animal digestive tract were determined. The presently reported study detected a total of 1596 parasitic worms: digeneans (1086), tapeworms (410) and nematodes (100). Acanthocephalans were not found. Even though only a few goosanders were examined, the results show a high species richness of parasite assemblages consisting of 22 species, representing 21 genera. The following were deemed as definite dominants (superdominants): Diplostomum mergi Dubois, 1932; D. pusillum (Dubois, 1928); Microsomacanthus abortiva (von Linstow, 1904) and Schistocephalus solidus (Müller, 1776). Helminths were found in all birds with their great relative density and intensity of occurrence (266 parasites on average). As expected, the parasite assemblages were characterized by considerable topical specificity, probably resulting from the feeding preferences of the worms. The majority of helminths, including predominant part of flatworms, were found in duodenum and jejunum of ducks. Nematodes, on the other hand, colonized mainly the gizzard and proventriculus
