LMBV found in Upper Mississippi River
U.S. Fish and Wildlife

The U.S. Fish and Wildlife Service's La Crosse Fish Health Center identified largemouth bass virus during annual sampling in Pools 3 and 7 of the Upper Mississippi River. The Service and its partners are working together to determine how widespread the virus is. But biologists note that, based on existing information, fish are safe for consumption.  

This is the first confirmation of the virus in Minnesota and Wisconsin waters. Pool 3 is located in a stretch of the river between Hastings and Red Wing, both in Minnesota, and Pool 7 stretches from Trempealeau to just north of LaCrosse, both in Wisconsin.   The virus was found in smallmouth bass taken from Pool 3, as well as white bass, rock bass, largemouth and smallmouth bass in Pool 7. Fish samples tested from Pools 4 and 9 show no sign of the virus to date, and none of the fish show signs of disease. The Service and its partners will continue routine monitoring of fish health in future surveys.  

"We're still in the early stages of determining what this virus means to the bass populations in the Mississippi River," Rick Nelson, Fish Health Center project leader, said. "But we are continuing our work with the states to monitor for its impact."   The Fish Health Center staff and its partners identified presence of the virus while performing annual fish health sampling for the National Wild Fish Health Survey. The survey began in 1997 and identifies disease in wild fish and monitors its distribution throughout the country.  

It's currently unknown how prevalent this virus is in wild populations, or the effect the virus has on bass populations. Extensive testing has only begun within the last few years and more study is required to determine range and effects in wild populations.  Nelson said, "Largemouth bass virus is one of more than 100 naturally occurring viruses that affect fish, but not warm-blooded animals. The virus was first identified in 1995 from a South Carolina reservoir with a large number of fish that had died. Biologists linked the fish kill to the largemouth bass virus and have since located this virus in 17 states, including Illinois, Indiana, and Michigan in the Midwest, he said. "This is the first confirmed case of this virus in Minnesota and Wisconsin."  

After the River fish tested positive, Service biologists tested bass from Genoa National Fish Hatchery, Wis. The hatchery holds adult fish that originated from the river, in its ponds for use with native freshwater mussel restoration. The virus was found in smallmouth bass adults and fingerlings, and largemouth bass adults. Plans are being made to replace these fish with fish from disease-free sources.   The Minnesota Department of Natural Resources noted that they have not detected largemouth bass virus in more than two years of monitoring brood stock at the state hatchery in New London, and that they continue to monitor up to 12 private hatcheries in the state for the virus and more serious disease.  

According to the Minnesota DNR there have been no reports of fish kills in Minnesota that could be linked to largemouth bass virus and that fish susceptible to disease are tested as a matter of procedure.   DNR Pathologist Joe Marcino, said, "We've had the ability to test for the virus for some time, but haven't had occasion to use it in relation to a fish kill. We do monitor reports of fish kills and are prepared to test if we find evidence of largemouth bass virus."  According to Nelson, this particular virus is often found in bass that show no signs of the disease. "This suggests that some fish might be infected but never become ill. And it is important to note that presence of the virus does not necessarily mean that a fish disease is occurring. Disease is more likely triggered by stress."  

Nelson indicated that some of the stressors could include extremely warm water, poor water quality, or repeated handling of the fish, and that none of the fish tested were showing any sign of the disease.   "Fish that develop largemouth bass virus appear near the surface and have trouble swimming and remaining upright," Nelson said. "This virus seems to attack the swim bladder in the affected fish."  

Susan Marcquenski, fish health specialist for the Wisconsin Department of Natural Resources, plans to collaborate with the LaCrosse Fish Health Center in 2003 to sample smallmouth and largemouth bass populations in tributaries to the Mississippi River.   "Wisconsin DNR fisheries biologists will collect fish from these tributaries and the fish will be examined for largemouth bass virus as well as other pathogens by the LaCrosse Fish Health Center staff," she said. "The national wild fish health survey has built a great partnership between our agencies.  

The Wisconsin DNR fish health program does not have the resources to do intensive health monitoring of wild fish populations on an extensive geographic basis. However, in partnership with the U.S. Fish and Wildlife Service, we can pool our resources and obtain meaningful information about the health of wild fish in the state."   The Fish Health Center in LaCrosse works to keep fish disease-free at six National Fish Hatcheries and three tribal facilities. They provide lab services and technical assistance on fish health and propagation to the U.S. Fish and Wildlife Service's field offices in the Great Lakes-Big Rivers Region (Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio and Wisconsin), tribes, states, commercial fisheries managers, universities and other research agencies. Efforts by the Service and its fisheries partners help insure strong, healthy and abundant fish throughout Midwest fisheries.   Nelson said, "Our staff at the Fish Health Center screens about 4,400 fish as part of the National Wild Fish Heath Survey. Each year we also inspect the health of more than 2.5 million captive lake trout produced in the region for eventual stocking in the Great Lakes."