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Acta Parasitologica, Vol.46, No. 4, 2001, 261-266
Karlsbakk Egil - Aspects of the morphology and ecology of Otodistomum (Digenea, Azygiidae) metacercariae in an intermediate host, Enchelyopus cimbrius (Pisces, Phycidae).

Department of Fisheries and Marine Biology, University of Bergen, Bergen High Technology Centre, P.O. Box 7800, N-5020 Bergen, Norway
(most of this work performed at the Zoological Institute, University of Bergen, Allégaten 41, N-5007 Bergen, Norway)

Otodistomum infections in an intermediate fish host, Enchelyopus cimbrius (L.), were investigated through one year in Raunefjorden, western Norway. The morphology and growth of the Otodistomum metacercariae is discussed in relation to previous knowledge on these metacercariae in north Atlantic fishes. The evidence suggests they are juvenile Otodistomum cestoides (van Beneden, 1871). The distribution of the metacercariae in the host is described. No seasonal patterns in infection were apparent, but prevalence and abundance increased with host size. This increase occurred mainly in the larger size-classes (> ca. 20 cm), but a stable persistent infection was present in smaller fish. It is suggested that E. cimbrius is first infected as juveniles, and that further accumulation is associated with piscivory. Intensities were low, with a maximum of 10 metacercariae per fish. Despite this, two lines of evidence suggest that parasite-induced host mortality does occur in this host-parasite system. There is a decrease in over-dispersion in the largest (oldest) fish, and a negative correlation of host condition with parasite load. Therefore, it is suggested that heavy Otodistomum cestoides metacercarial infections may affect the survival of small hosts.

KEY WORDS: Otodistomum, metacercariae, Digenea, morphology, growth, ecology, effects, Enchelyopus cimbrius, marine fish, Norway
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