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

centrarchids, percids, and cyprinids and their autogenic helminths, followed by the catostomids
and salmonids and their autogenic parasites.
In general, fish species in the five major families examined for parasites were different among the
Great Lakes. Percids were most commonly examined in Lake Michigan, salmonids in Lake
Superior, cyprinids in Lake Huron, and centrarchids and percids in Lakes Erie and Ontario. The
common thread among these lakes is that percid parasites were the most-dominant group or the
second most-dominant group in each lake probably because of the large number of studies and/or
extensive survey(s) performed on the parasites of Perca flavescens. Perca flavescens had the
highest parasite species-richness in each Great Lake, except for Coregonus artedi in Lake
Superior. Because there was variation in the fish species examined among the Great Lakes, the
reported parasite communities in fish from each lake were different, and therefore the Jaccard
coefficients are low for the parasite-community comparisons.
It is probable that, as the number of fish species examined and number of parasite studies
performed increases, so will the number of parasite species found in each Great Lake, especially
those parasite species that are host-specific to a fish species or fish family. Although not
significant, correlations were high between the number of parasite species reported from each
lake and number of fish species examined and number of parasite studies performed.
Furthermore, some of these parasitological results summarized in this synopsis for each Great
Lake may be artifacts of sample size, may be influenced by the number of individuals of various
fish species examined, may be affected by the number or lack of studies performed on specific
fish species, and may be biased by the lack of studies on other fish species.
Conceptual Framework to Study Fish Health in the Great Lakes
Riley et al. (2008) proposed a conceptual framework for conducting ecologically oriented fish
health research in the Great Lakes. Their premise was that a dysfunctional ecosystem, one that
has been disrupted to reduce vigor, organization, or resilience, may show a wider range of
variability to factors that influence disease transmission, thereby increasing the likelihood that the
threshold required for epizootics will be exceeded. The material they presented focused on
viruses and bacteria of fish, and they discussed three models involving thiamine deficiency
complex, botulism, and bacterial kidney disease in the Great Lakes.
A possible example of parasites and a dysfunctional ecosystem involves the occurrence of
cestodes, especially of the genera Bothriocephalus and Proteocephalus, in Sander vitreus in
Saginaw Bay, Lake Huron. These cestodes use copepod zooplankton as the first intermediate host
and small fish as the second intermediate host or as the paratenic host. Sander vitreus and other
fish species become infected by eating the infected copepods or small fish. In 2007, there were
numerous angler reports of an increased prevalence of cestodes in Sander vitreus from Saginaw
Bay and its tributaries (J. Baker, Michigan Department of Natural Resources and the
Environment, personal communication, 2007 and 2008). It was suggested that biological
conditions in Saginaw Bay (specifically, changes in the food chain) in 2007 may have changed to
make the cestode infection in Sander vitreus more prevalent than in previous years. The increased
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