Digenetic trematodes fromGadus morhuaL. (Osteichthyes, Gadidae) from Danish and adjacent waters, with special reference to their life-histories

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Abstract
A total of 890 specimens of the Atlantic cod Gadus morhua L. (Osteichthyes, Gadidae) have been examined for infestations with digenetic trematodes. The cods were caught at 15 sampling stations in Danish and adjacent waters with salinities ranging from 8‰ (the Baltic off Bornholm) to 35‰ (the North Sea and the Atlantic Ocean off the Faroes), and from shallow water down to a depth of 230 m. 18 species (metacercariae and adults) were found. The following species were found in the alimentary tract: Prosorhynchus squamatus Odhner, 1905 (Bucephalidae), Podocotyle atomon (Rudolphi, 1802), P. reflexa (Creplin, 1825) (Opecoelidae), Lepidapedon elongatum (Lebour, 1908), L. rachion (Cobbold, 1858), Opechona bacillaris (Molin, 1859) (Lepocreadiidae), Stephanostomum pristis (Deslongchamps, 1824) (Acanthocolpidae), Derogenes varicus (Müller & 1784), Lecithaster gibbosus (Rudolphi, 1802), Brachyphallus crenatus (Rudolphi, 1802), Hemiurus communis Odhner, 1905, H. luehei Odhner, 1905, H. levinseni Odhner, 1905, immature encapsulated Lecithochirium sp. (Hemiuridae), and the metacercaria of Otodistomum sp. (Azygiidae). The metacercaria of Bucephaloides gracilescens (Rudolphi, 1819) (Bucephalidae) was found in the brain cavity, the metacercaria of Diplostomum spathaceum (Rudolphi, 1819) (Diplostomatidae) was found in the eye lens, and the metacercaria of Cryptocotyle lingua (Creplin, 1825) (Heterophyidae) occurred in the skin throughout the fish body. O. bacillaris, H. luehei and Lecithochirium sp. have not previously been reported from the cod. The infestation in relation to host size of the most common cod digeneans was examined. The incidence of infestation at all stations is compared with the geographical distribution of the first intermediate host (when known) to examine whether the digeneans may be used as natural tags. The number of digenean species increased from the Baltic to the northern Øresund and the western Kattegat, where it reached a maximum value, then decreased again in the North Sea and Faroese waters, reflecting the different diversity of the benthic fauna in the different areas.