VHS fish disease caused gizzard shad fish kill in Milwaukee Harbor ship canals

MILWAUKEE – A mid-March fish kill of thousands of gizzard shad
in the Milwaukee Harbor ship canals was caused by the fish virus
viral hemorrhagic septicemia, or VHS, according to results released
March 31 from the Wisconsin Veterinary Diagnostic Laboratory in
Madison.

The finding represents the first time VHS has been detected in
Wisconsin’s waters of Lake Michigan since 2008, and the first time
gizzard shad have tested positive for VHS in Wisconsin, according
to Sue Marcquenski, Department of Natural Resources fish health
specialist.

“The results show that the virus is persisting in the
environment, and as some have predicted, new isolations of the
disease will likely be from younger year-classes of fish that
haven’t built up immunity to the virus,” she said.

VHS, which can infect several dozen different native fish
species and cause them to bleed to death, does not affect humans.
The first detection of the virus was in freshwater drum from the
Lake Winnebago system in 2007, and also in Wisconsin’s waters of
Lake Michigan that same year. The virus was first confirmed in Lake
Superior in 2010 from samples of lake herring.

The Milwaukee Harbor canals fish kill started the week of March
14 and by March 18, involved several thousand fish. Dead and dying
gizzard shad were collected and necropsied on March 22 and
submitted to the Madison laboratory for testing, Marcquenski
said.

DNR will be testing fish from 27 waters this spring as part of
its surveillance program for VHS and also to assure that the
disease is not present in those rivers that DNR relies on for water
supplies for its hatcheries.

Infected fish shed the virus in their urine and reproductive
fluids and the virus can survive in water for at least 14 days.
Fish also can be infected when they eat an infected fish.

“The important message here is VHS is still out there and we
have to be vigilant about cleaning our boats and not moving fish
around,” says Al Kaas, DNR fish hatchery operations chief. These
steps also will prevent the spread of other fish diseases and
invasive species like zebra mussels and spiny water fleas.

Under statewide VHS rules:

• Minnow harvesting of any kind is not allowed on any VHS
affected waters: Lake Michigan, Lake Superior, the Mississippi
River, Lake Winnebago, Fox River from Lake Winnebago to Green Bay,
and all connecting waters upstream to the first barrier impassible
to fish.

• Anglers and boaters must drain all water from the fishing and
boating equipment when leaving the lake or entering the state
(except drinking water and a small amount of water to move minnows
as described below).

• Anglers statewide may not move live fish or fish eggs away
from any water except minnows they bought from a registered
Wisconsin bait dealer and used under certain conditions. Such
leftover minnows can be used again on the same water, or can be
used elsewhere if the angler did not add lake or river water or
other fish to their bait container.

For more information on the fish disease and how to prevent its
spread visit DNR’s web page: http://dnr.wi.gov/fish/vhs/

 

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