A new fish disease could turn up in Minnesota waters. Viral hemorrhagic septicemia, or VHS virus, attacks both saltwater and freshwater fish, causing them to bleed to death.
It has shown up in all of the Great Lakes except Lake Superior, as well as in waters in other states, including Lake Winnebago in Wisconsin. It has caused fish kills in muskies, walleyes, lake whitefish, yellow perch, freshwater drum, and round gobies. It can also infect other freshwater game fish, including trout, crappies, bluegills, bass, and northern pike. Specific to fish, the virus does not pose any threat to human health.
VHS virus is transmitted from fish to fish, especially when fish are schooled together. It has been found on the surface of newly spawned eggs, so it can be transmitted between generations. Fish can also contract it through virus-contaminated water.
VHS was first described in Europe after rainbow trout imported from North America died in large numbers from unknown causes in the late 1930s. With advances in viral detection technology, scientists eventually isolated and identified the VHS virus in 1963. In 1988 it turned up in salmon and other marine fish in Pacific Northwest coastal waters. Then the virus appeared in marine fish on the Atlantic coast. Between 2002 and 2003, it appeared in Lake St. Clair, which connects Lake Huron and Lake Erie. Michigan DNR estimated that it killed 2 to 4 percent of the muskies in Lake St. Clair in March 2006. A 2006 fish kill in Lake Erie resulted in windrows of dead fish (mostly freshwater drum) on Ohio's shoreline.
Of the four recognized types of VHS, only one occurs in the Great Lakes. VHS could reach Minnesota through spread to Lake Superior from other Great Lakes, from the Mississippi River by way of the Chicago Sanitary and Ship Canal and the Illinois River, or through transport of fish, bait, or water from an infested body of water.
Minnesota DNR is conducting systematic field sampling and testing of susceptible fish species to improve the likelihood of catching VHS early and stopping its spread. Last fall, with a grant from the U.S. Department of Agriculture, the DNR tested fish taken from 31 water bodies, including Mille Lacs and Bowstring. None of the fish tested positive for VHS. Fish from another 59 water bodies, including Winnibigoshish, Lac qui Parle, and Minnetonka, are being tested this spring.
To reduce the risk of moving the disease inland if it reaches Lake Superior, DNR Fisheries has taken precautions, including discontinuing use of Superior and the St. Louis River estuary for fish hatching and rearing operations.
If you see fish that have red patches or pinpoint spots on their skin and appear listless, swimming in circles or hanging at the surface, call the DNR at 651-296-6157 or 888-646-6367.
Darryl Bathel, retired DNR trout production supervisor
Ron Payer, DNR Fisheries management section chief