Tests Reveal Cause Of Massive Fish Kill
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.