Friday, February 3rd, 2023
Friday, February 3rd, 2023

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VHS virus confirmed in Lake St. Clair fish

DNR Report

Mount Clemens, Mich. — The DNR has confirmed that viral
hemorrhagic septicemia (VHS), a virus that causes disease in fish
but does not pose any threat to public health, is present in
several fish species in Lake St. Clair. The virus also has been
detected in fish in the past year in Lake Ontario by the Ontario
Ministry of Natural Resources and New York Department of
Environmental Conservation, in Lake Erie by the Ohio Department of
Wildlife, and in the St. Lawrence River by the New York DEC.

The virus was detected by the DNR/MSU Aquatic Animal Health Unit
in muskies, yellow perch, gizzard shad, northern pike, silver
redhorse, and shorthead redhorse collected this past spring in Lake
St. Clair. DNR fisheries officials now believe VHS was a likely
factor in the deaths of muskies, yellow perch, and gizzard shad
observed last spring in the St. Clair River, Lake St. Clair, and
the Detroit River.

The timing of the die-offs corresponded with the end of the
stressful winter season for all fish species and the beginning of
spawning season for muskies. Spawning is extremely taxing and
creates additional stress on fish, thus making them more vulnerable
to infection and disease. VHS outbreaks tend to occur during the
spring season since the virus thrives at water temperatures between
40 and 60 degrees.

VHS also has affected fish elsewhere in the lower Great Lakes.
This past spring, 18 dead and dying muskies were collected in the
Thousand Islands region of the St. Lawrence River during the
spawning period. In addition, VHS is suspected as a factor in
large-scale mortalities of freshwater drum and yellow perch
observed in Lake Erie, and large numbers of round gobies that
perished in Lake Ontario this past spring.

There are at least four different strains of VHS. The virus has
been found in continental Europe, Japan, and both coasts of North
America. The European strain of this virus has been responsible for
large-scale losses in rainbow trout and turbot in fish farms.

Prior to 2005, VHS-related mortalities were limited in North
America to saltwater fish species such as Pacific herring and
pilchard from the Pacific Coast of North America and mummichogs in
Atlantic Ocean tributary streams. Systemic VHS infections have been
found in a range of North American fish including rainbow trout,
brown trout, lake trout, chinook salmon, and coho salmon, but
large-scale mortalities have not been documented to date.

In 2005, VHS was detected for the first time in Great Lakes fish
species in the U.S. and Canada, including muskies in Michigan’s
waters of Lake St. Clair and freshwater drum in Lake Ontario. It is
not known how VHS was transferred to the Great Lakes region or how
long it has been in the waterways of the Great Lakes, although a
re-analyzed sample from a muskie collected in Lake St. Clair in
2003 recently has tested positive for the virus.

It is not known what the long-term effects of this virus will be
in Michigan, DNR fisheries officials said.

“One likely possibility is that VHS will act like many other
viruses in the environment. Typically, viruses or bacteria infect
fish, which may lead to disease in the fish if they are
susceptible. Once the disease is expressed in these fish, a small
percentage will die,” said Kelley Smith, chief of the DNR Fisheries
Division. “The vast majority, however, will survive and will
develop immunity to the viruses or bacteria that cause a
disease.

“Since there are no large-scale treatments for VHS that can be
applied to fish in the wild, the presence of this new virus may
result in spring fish mortalities that are abnormally high for a
few years as more fish encounter the virus. These mortalities
should abate as fish begin to build immunity to the virus.”

Citizens are encouraged to report sick fish or fish kills to
their local DNR office or use the DNR web site at
www.michigan.gov/dnr. Anglers should contact the DNR if they
observe fish that exhibit any of the following signs: hemorrhaging
in the skin, including large red patches particularly on the sides
and anterior portion of the head; multiple hemorrhages on the
liver, spleen, or intestines; or hemorrhages on the swim bladder
that give the otherwise transparent organ a mottled appearance.
This information will help DNR fisheries staff track VHS and take
appropriate management actions to help slow the spread of this
virus.

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