Abstract:Hornsund, an Arctic fjord in the west coast of Spitsbergen (Svalbard), was se− lected as All Taxa Biodiversity Inventory (ATBI) site under EU 5th Framework Concerted Action BIOMARE (2000)(2001)(2002), especially due to its pristine, undisturbed natural charac− ter. On the base of large material (89 stations located throughout the fjord and 129 Van Veen grab samples) collected during cruises of RV Oceania in July in 2002, 2003, 2005 and 2007 and literature search a comprehensive list of species recorded within Hornsund area, on the soft bottom with depth range of 30-250 m is provided. Over 220 species were identified in− cluding 93 species of Polychaeta, 62 species of Mollusca and 58 species of Crustacea. Spe− cies list is supported by information on the zoogeographical status, body length and biologi− cal traits of dominant species. Need for further research on Hornsund soft bottom fauna with more sampling effort is highlighted.

Adult stages of digenean flukes are usually well studied, but their larval forms, the metacercariae, do not receive comparable attention of researchers. As a consequence, metacercariae, especially small ones, are routinely overlooked, despite their serious epidemiological and epizootic potential. Therefore, the existing distribution data are patchy and the biogeographic knowledge is far from being complete. We were not able to trace any papers focusing on the depth of penetration of digenean metacercariae in fish tissues. There have been almost no surveys on the metacercariae density (ind. • g-1) in fish muscles. In this study, we were trying to determine the spatial distribution of metacercariae in the muscles of two freshwater cyprinid fishes, the roach, Rutilus rutilus (Linnaeus, 1758) and the bleak, Alburnus alburnus (Linnaeus, 1758). The study area was Lake Dąbie, a large and shallow deltaic lake of the Oder (Odra) River estuary, Poland. We studied a total of 40 roach (12.0-21.5 cm TL 30-120 g TW) and 15 bleak (10.5-14.5 cm TL). The fishes were filleted and each filet was divided into four parts. All muscle tissues were examined for the presence of metacercariae using a trichinoscope and a dissecting microscope. Dorsal muscles of an additional 12 roach were sliced and the depth of metacercariae penetration was assessed. The dominant muscle parasite was Paracoenogonimus ovatus. Metacercariae of other species (Posthodiplostomum cuticula and Apophallus muehlingi) were only sporadically found in muscles roach and bleak (with a preference to the shin). The prevalence of P. ovatus in roach ranged from 66.7% to 100% and the highest infection intensity was 1973 specimens in one fish. The majority of metacercariae (354 out of 363) were found in the outer 50% of the muscle depth. The infection parameters differed between length classes of roach with the class 14.0-15.9 being infected in 100%. The presently reported finding of Paracoenogonimus ovatus in bleak, Alburnus alburnus, constitutes a new hosts record.