Comparative Parasitology 67(2) 2000 - Peru State College

Table 2. Continued.
Parasite
Trichodina sp.
Mastigophora
Ichthyobodo sp.
Farm
number,
year
1, 96
1, 96
2, 96
4, 96
4, 96
1, 97
1, 97
1, 97
7, 98
9, 98
11, 98
12, 98
1, 96
1, 96
1, 97
1, 98
8, 98
12, 98
3, 96
Trout
species*
OM
OM
OM
OM
OM
OM
OM
OM
OM
OM
OM
OM
SF
SF
SF
SF
SF
SF
OM
No. examined
10
24
12
13
25
10
20
5
20
18
22
11
20
10
12
19
6
2
20
MUZZALL—PARASITES OF TROUT 185
Prevalence
No. infected Mean intensity
(%) ±SD (max)
10 (100) —
14 (58)
3 (25)
2(15)
7(28)
3 (30)
2(10)
1 (20)
4 (20)
10 (56)
4(18)
2(18)
5 (25)
10 (100)
5 (42)
5 (26)
2(33)
1 (50)
2 (10) —
OM = Oncorhynchus mykiss; SF = Salvelinus fontinalis; ST = Salmo trutta.
Myxobolus cerebralis has been present in
Michigan waters since at least 1968, when it was
discovered in 3 commercial trout hatcheries.
Yoder (1972) discussed the spread of M. cerebralis
into native trout populations in the Tobacco
River, Michigan, from 1 of these hatcheries.
The protozoan spread down the first 6 mi of water,
and factors involved in this spread were the
high incidence of disease at the hatchery, abundance
of susceptible trout, and trout movement.
In 1998 and 1999, M. cerebralis was reported
from at least 6 privately owned trout farms in
Michigan. It has been suggested that it was endemic
in 1 or more facilities and transferred to
other facilities with infected fish or by piscivorous
birds that ate infected fish. In the present
study, M. cerebralis-infected trout were detected
in 3 farms. Infected trout, however, did not
have clinical symptoms. Furthermore, Sutherland
(1999) reported that M. cerebralis has been
found in fish from the Au Sable and Manistee
rivers in lower Michigan.
In the present study, parasites and their numbers
infecting trout in a pond may dramatically
change the next time the fish are sampled and
examined. One reason for this is that trout are
moved into and out of facilities during the year.
An example of this was evident at 1 farm, when,
Mean abundance
±SD
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in March 1997, 4 parasite species infected trout
and 2 were common (Table 4). In July, only 1
species infrequently infected trout after the infected
trout were moved out and uninfected ones
were moved in. Also, informing the owner of
the facility on the parasites found can affect infection
levels from 1 sampling date to the next.
After an owner was informed that brook trout
were infested with S. edwardsii, he told me that
"a treatment had been done to the pond." Approximately
2 months later, the prevalence and
mean intensity of S. edwardsii on trout from the
same pond were dramatically reduced. Another
suggestion for these differences is that parasite
species may exhibit a seasonal cycle in their occurrence.
Hare and Frantsi (1974) found 12 parasite
species, 10 parasite species, and 1 parasite species
infecting, respectively, Atlantic salmon,
Salmo solar Linnaeus, 1758; brook trout; and
rainbow trout, in 13 Canadian hatcheries in the
Maritime provinces. Hexamita salmonis (Moore,
1923) Wenyon, 1926; Trichophyra piscium
Buetschli, 1889; Diplostomum spathaceum (Rudolphi,
1819) Braun, 1893; Acanthocephalus later
alls (Leidy, 1851); and S. edwardsii were
considered to be serious fish pathogens, based
on the work of other authors. Buchmann and
Copyright © 2011, The Helminthological Society of Washington
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