Comparative Parasitology 67(2) 2000 - Peru State College

ter and fiberglass or concrete ponds and tanks
will also reduce the incidence of parasites.
The effects of natural bodies of water and the
fish in them serving as a source of parasites in
culture should be addressed. This involves facilities
with "flow-through" systems (those that
receive water from lentic or lotic environments).
Eggs, other infective stages, and hosts can be
carried with water that flows into and through
facilities. Obviously this facilitates infection of
fish. In general, trout in the present study being
raised in flow-through systems had more parasite
species and more individuals of the species
present in comparison with the other systems.
Similarly, Valtonen and Koskivaara (1994),
studying the relationships between parasites of
wild and cultured fishes in 2 lakes and a fish
farm in Finland, reported that the source of parasites
in the fish farm was the water-supplying
lake.
Cone and Cusack (1988) reported on the occurrence
of 2 monogeneans, Gyrodactylus colemanensis
Mizelle and Kritsky, 1967, and Gyrodactylus
salmonis Yin and Sproston, 1948, on
brook and rainbow trout, and Atlantic salmon,
Salmo salar Linnaeus, 1758, in a farm in Nova
Scotia, Canada, and discussed the origins of infection
and their dispersal in the farm. Sources
of infection with G. salmonis were stocks of infected
rainbow trout brought into the facility
from another farm, as well as wild infected Atlantic
salmon and brook trout gaining access to
the hatchery. Parasite dispersal in the farm involved
infected fish jumping and wriggling from
one pond to the next and the workers using
transfer nets and buckets that contained live parasites.
Also, brood stocks were infected and constituted
internal reservoirs of infection.
The effects of fish culture on natural waters
receiving water from the farms has been a subject
of increasing debate. If surveillance of parasites
in the water above and below the fish facility
is not continuous, little will be known
about where the parasite really originated or
how long it has been present. Regarding M. cerebralis,
fish known to have whirling disease
were imported into a commercial trout farm in
Michigan in 1968. The receiving stream (a
brook and brown trout stream) of this facility
yielded M. cerefera/zs—infected rainbow trout escapees
directly below the positive facility effluent.
Valtonen and Koskivaara (1994) suggested
that the farm itself was unlikely to affect the fish
MUZZALL—PARASITES OF TROUT 187
parasite fauna of the water-recipient lake, although
some ectoparasites could originate from
the farm.
Muzzall (1995c), studying the parasites of
pond-reared yellow perch, Perca flavescens
(Mitchill, 1814) in Michigan, suggested that
conditions of a pond associated with producing
a good crop of fish also support a good crop of
helminths that infect fish. Later, Muzzall (1996)
referred to this as "the good fish crop-good helminth
crop" relationship. Based on the results
of the parasites infecting trout in the present
study, this relationship does not occur. Of the
parasite species found by Muzzall (1995c) infecting
perch, 8 were represented as only larval
stages, 6 of which were digenetic trematodes.
Only 2 genera (generalist protozoans, Trichodina
sp., Capriniana sp.) infesting perch were also
found infesting trout. The dramatic differences
in parasites found in yellow perch and trout from
culture conditions can be explained by many
factors. Probably the most important are the
types of ponds used to culture the particular species,
water temperatures, water sources, whether
ponds are periodically drained, the surroundings
of the ponds, and animals associated with the
ponds.
The state of control and prevention of parasites
and diseases of fishes in culture in Michigan
is difficult to assess. I refer to it as "crisis
fisheries health," which can be defined as follows:
"Some state and university officials, extension
specialists, aquaculture centers, and trout
farmers are not apparently concerned with fish
health in aquaculture and in nature unless there
is a crisis health problem, then action takes
place." This approach is understandable with so
many interested parties having different motives
and the low priority of funding for parasite and
disease work. I suggest that more studies on fish
parasites and diseases in Michigan be encouraged
and supported by the interested groups.
Surveillance and surveys are needed to determine
what parasites are infecting trout in culture
conditions and in the surrounding waters.
As mentioned earlier, growers in Michigan are
involved in 3 activities in producing and selling
trout. In regard to the first, the sale of infected
trout for stocking could transfer some parasites
to other fish directly or contaminate the watershed
with other parasites. However, most if not
all parasites reported in this study have been
found infecting trout in the wild. Second, no par-
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