Parasites of Fish from the Great Lakes - Great Lakes Fishery ...

Nematodes
Hysterothylacium brachyurum and Raphidascaris acus are large nematodes infecting the
digestive tract, but their pathological effect on fish is unknown. Cystidicola farionis infected the
swim bladder of salmonids and Osmerus mordax, while C. stigmatura infected S. namaycush.
Black (1984) reported swim bladder lesions associated with Cystidicola stigmatura in Salvelinus
namaycush. Willers et al. (1991) and Knudsen et al. (2002) reported on histopathological changes
of swim bladders infected with Cystidicola farionis and believed this nematode may cause
mortality to the most heavily infected Salvelinus alpinus. Adults of Philometra cylindracea that
occur in several non-intestinal sites may play a role in reduced growth and high mortality of
Perca flavescens (see Allison 1966; Crites 1982; Salz 1989).
Larvae of Contracaecum sp. (mesentery), Hysterothylacium brachyurum (liver), Raphidascaris
acus (liver, spleen), Raphidascaris sp. (free and encapsulated in liver, mesentery, and intestinal
wall), Camallanus oxycephalus (encysted), Camallanus sp. (liver, gonads), Eustrongylides tubifex
(mesentery, muscle), Eustrongylides sp. (body cavity, viscera), Spiroxys contortus (mesentery),
Spiroxys sp. (mesentery), and Philometra sp. (mesentery) can cause inflammation to the viscera
and other sites and possibly increase the fish’s susceptibility to secondary infections by viruses,
bacteria, and fungi. Larvae of Eustrongylides tubifex may play a role in reduced growth and high
mortality of Perca flavescens (see Allison 1966; Crites 1982; Salz 1989). Crites (1982) suggested
that high intensities of Eustrongylides tubifex resulted in lower mean weight in infected ageclasses
of Perca flavescens. Salz (1989) demonstrated that water content was consistently higher
in the viscera of Perca flavescens infected with Eustrongylides tubifex than in fish not infected,
indicating that E. tubifex may utilize some of its host’s lipid reserve.
Acanthocephalans
The adult acanthocephalans (Acanthocephalus dirus, Echinorhynchus salmonis, Pomphorhynchus
bulbocolli, Leptorhynchoides thecatus) can reduce the absorption of nutrients in infected fish
(Bullock 1963; Schmidt et al. 1974). McDonough and Gleason (1981) reported that
Pomphorhynchus bulbocolli caused the formation of a fibrous capsule around its proboscis when
it penetrated the intestinal wall. Echinorhynchus salmonis, Pomphorhynchus bulbocolli, and L.
thecatus also occurred encysted in a variety of non-intestinal sites causing inflammation and
fibrosis.
Leeches
Leeches on Lake Huron fishes had low prevalences and/or intensities and are of minor pathologic
importance to fishes, except possibly for Actinobdella inequiannulata that has been reported to
cause damage to the gills and operculum of catostomids (Dechtiar and Lawrie 1988).
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