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

Cestodes
Several adult cestodes (Eubothrium salvelini, Cyathocephalus truncatus, Triaenophorus
nodulosus, Triaenophorus stizostedionis) can be considered pathogens of fish by causing
inflammation of the intestinal epithelium, disruption of the mucosa, and rupture of blood vessels
at point of attachment. Eubothrium salvelini retarded the growth and condition factor, caused
poor swimming performance, and caused aberrant behavior of Oncorhynchus nerka, thereby
increasing susceptibility to predation (Smith and Margolis 1970; Smith 1973; Boyce 1979).
Eubothrium salvelini also reduced condition factor in Salvelinus alpinus (see Hoffman et al.
1986). Vik (1958) reported that Cyathocephalus truncatus caused the distension and perforation
of the ceca and also mortality of trout. Proteocephalus exiguus and P. laruei were possibly
involved in the mortality of young coregonines (Nümann 1972).
Plerocercoids of Diphyllobothrium ditremum, D. laruei, Proteocephalus ambloplitis,
Triaenophorus nodulosus, and T. stizostedionis can be pathogenic to fish. Duguid and Sheppard
(1944) and Hoffman and Dunbar (1961) reported that Diphyllobothrium sp. caused an epizootic
in Salvelinus fontinalis and S. alpinus. A major decline of Salmo trutta and Salvelinus alpinus in
Norway was caused by Diphyllobothrium sp. (Vik 1965). Plerocercoids of Proteocephalus
ambloplitis can cause severe damage to gonads, liver, spleen, and mesentery of Micropterus spp.
and other fish species (Bangham 1972; Dechtiar 1972a; Esch and Huffines 1973; McCormick and
Stokes 1982). Esch and Huffines (1973) and McCormick and Stokes (1982) demonstrated that the
plerocercoids of Proteocephalus ambloplitis in female Micropterus dolomieu reduced their
reproductive capacity by loss of oogenic tissue caused by scarring of ovaries, fibrosis, and direct
oocyte destruction. Stromberg and Crites (1974a) reported that plerocercoids of Triaenophorus
nodulosus infecting the mesentery and liver of Morone chrysops caused an acute inflammatory
response, hemorrhage, liver necrosis, squamous metaplasia, fibrosis, and liver tissue
displacement. Furthermore, Dechtiar and Christie (1988) reported that the livers of Morone
chrysops had moderate to heavy infection of Triaenophorus nodulosus, causing serious problems.
Nematodes
Black (1984) reported that lesions of the swim bladder of Salvelinus namaycush may develop as a
result of chronic mechanical irritation caused by mature Cystidicola stigmatura. Lankester and
Smith (1980) reported that Cystidicola farionis caused raised ulcers in the swim bladders of
Oncorhynchus mykiss. Willers et al. (1991) and Knudsen et al. (2002) reported histopathological
changes in swim bladders of Salvelinus alpinus infected with Cystidicola farionis.
Larvae of several nematodes (Cosmocephalus obvelatus, Paracuaria adunca, Contracaecum
spiculigerum, Hysterothylacium brachyurum, Hysterothylacium sp. Eustrongylides tubifex,
Spiroxys sp., and Philometra cylindracea) can cause problems and damage to a variety of nonintestinal
sites in fishes when they occur in high intensities, and encysted or non-encysted.
Eustrongylides tubifex, commonly called the large redworm, can cause the formation of large
capsules in infected fish. Crites (1982) indicated that the larvae of Eustrongylides tubifex become
encapsulated by the tissues of the organs they penetrate. He further suggested there is evidence
that as these capsules in the body wall continue to grow and enlarge they put pressure on the
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