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

The percentages of cestodes varied from 12% in Lakes Huron, Erie, and Ontario to 17% in Lake
Michigan. The percentages of nematodes ranged from 9% in Lake Ontario to 14% in Lakes
Michigan and Superior. The percentages of acanthocephalans varied from 6% in Lakes Erie and
Ontario to 9% in Lakes Michigan and Superior. Leeches varied from 1% in Lake Huron to 5% in
Lake Michigan. Copepods varied from 4% in Lake Ontario to 8% in Lake Michigan. Mollusc
species made up 1% or less of all the parasite groups in each lake.
The percentage occurrence of the major parasite groups in the five major fish families
(Cyprinidae, Catostomidae, Centrarchidae, Percidae, Salmonidae) varied among the lakes (Tables
6, 10, 16, 22, 28). For the cyprinids, the digenetic trematodes were the dominant group in Lakes
Superior and Erie, and the monogeneans were the dominant group in Lakes Huron and Ontario.
Protozoans, specifically the myxozoans, were most-common group in Lake Michigan cyprinids.
In the catostomids, the acanthocephalans dominated in Lake Michigan, the digenetic trematodes
were most common in Lakes Superior (tied with cestodes) and Huron, and the monogeneans were
most common in Lakes Erie and Ontario.The digenetic trematodes were the dominant parasites in
the centrarchids in Lakes Michigan, Superior, Huron (tied with monogeneans), and Erie (tied with
monogeneans), and were the second most-common group following the monogeneans in Lake
Ontario. For the percids, digenetic trematodes were the most common group in Lakes Michigan
(tied with the nematodes) Superior, Huron, Erie, and Ontario. Cestodes were the dominant group
in salmonids from Lakes Superior, Erie, and Ontario. Copepods were most numerous in
salmonids in Lake Michigan followed by cestodes and nematodes, and nematodes were most
common from Lake Huron followed by cestodes, acanthocephalans, and copepods.
Rearranging the above parasite group information by lake, digenetic trematodes were the mostcommon
group of parasites infecting centrarchids and percids in all the lakes, except they ranked
second to monogeneans for the centrarchids in Lake Ontario. This information indicates that the
centrarchids and percids more often than the other fish families use shallower and warmer
habitats during warm-weather periods where and when the mollusc snail intermediate hosts are
present. Furthermore, the digenetic trematodes or monogeneans were the most-common parasite
groups in Lake Huron and in the cyprinids and catostomids from Lakes Erie and Ontario.
Fish in each of the five families from each Great Lake were characterized by their temperature
preferences. A general trend is that warm- and cool-water fish have more digenetic trematodes
and monogeneans than the cold-water fish. Also, digenetic trematodes are the most-common
parasite group in centrarchids and percids in most of the Great Lakes, which indicates that fish in
these families share similar habitats in the lakes where they are exposed to digenetic trematodes
as well as with the mollusc intermediate hosts used by the digenetic trematodes.
Digenetic trematodes or monogeneans were never the most-common parasite group in salmonids
because salmonids are cold-water species in all the lakes. The salmonid parasite community is
instead dominated by cestodes, nematodes, or acanthocephalans. This infrequency of digenetic
trematodes and monogeneans is due to the occurrence of salmonids in deep, cold-water habitat
during warm-weather periods where mollusc intermediate hosts for digenetic trematode are
absent or infrequent, and this habitat is not conducive for the occurrence of many monogeneans
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