During this time 24 flounders were examined parasitologically. The fish were dissected and following organs were examined: skin and fins, eyes, gills, body cavity, liver, kidney and digestive tract. Parasites found were identified microscopically and fixed in 70 % ethanol. Samples of fish were taken mostly from commercial catches in two areas near Hiiumaa: Suuresadama and Kôrgessaare (Fig. 1, page 12) The species found in autumn are named in Table 2 (page 14); the intencity of invasion in Table 3 (page 15). The species found in spring are named in Table 4 ( Page 17) and the intencity of invasion in Table 5 ( page 19). At the present study 10 helminth species were found in the costal waters of Western Estonia; belonging to the following systematic groups: Nematoda Dichelyne (Cucullanellus) minutus, Cucullanus heterochrous, Contracaecum osculatum, Raphidascaris acus; Trematoda Diplostomum spathaceum, Cryptocotyle concava;
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