Largemouth Bass Virus Continues to Spread in Michigan Waters

Contact: Gary Whelan 517-373-6948
Agency: Natural Resources

May 24, 2004

LANSING--State fisheries officials today announced that Largemouth Bass Virus continues to spread in southern Michigan lakes, and called upon anglers to help contain the disease and protect fish populations.

Largemouth Bass Virus (LMBV) is one of more than 100 naturally occurring viruses that affect fish, and is closely related to viruses found in frogs and other amphibians. Its origin and how it is spread are unknown. The virus is not known to infect humans, and infected fish are considered safe to eat. However, it is recommended that all fish should be thoroughly cooked as a precaution.

In the fall of 2000, biologists from the Michigan and Indiana Departments of Natural Resources discovered the presence of LMBV while jointly investigating a die-off of largemouth bass in Lake George, located on the Michigan-Indiana border near I-69.

The discovery marked the first time LMBV had been detected in either Michigan or Indiana and was the furthest north that the virus had been detected in the United States. It was first discovered in the Santee-Cooper Reservoir of South Carolina in 1995, following a die-off of largemouth bass. Since then, the virus has been detected in wild fish from 17 states including Indiana, Illinois and Michigan.

The Department of Natural Resources began actively surveying lakes in Southern Michigan for LMBV in 2002 and continued in 2003. Based on these and earlier data, the virus has been confirmed in 15 of 30 lakes examined. These lakes are as follows:

  • Lake George, Branch County - found in 90% of 2000 samples but not detected in 2002 samples.
  • Long Lake, Hillsdale County (near Camden) - found in 2001 samples
  • Klinger Lake, St. Joseph County - found in 2001 samples and 60.6% of the 2003 samples
  • Long Lake, St. Joseph County - found in 2001 samples
  • Austin Lake, Kalamazoo County - found in 2002 samples and in 25.4% of 2003 samples with high levels of the pathogen in positive fish
  • Woodland Lake, Livingston County - found in 100% of 2002 samples and 60% of 2003 samples with high levels of the pathogen in positive fish
  • Saddle Lake, Van Buren County - found in 2002 samples
  • Lake Orion, Oakland County - found in 6.3% of 2002 samples and 48% of 2003 samples with low levels of the pathogen in positive fish
  • Devils Lake, Lenawee County - found in 14.3% of 2002 samples
  • Lake Ovid, Clinton County - found in 45.8% of 2003 samples with medium levels of the pathogen
  • Duck Lake, Calhoun County - found in 27.8% of 2003 samples with medium levels of the pathogen
  • Sand Lake, Lenawee County - found in 44.4% of 2003 samples with low levels of the pathogen
  • Sanford Lake, Midland County - found in 100% of 2003 samples
  • Lake St. Clair, St. Clair County - found in 100% of the 2003 samples
  • Baseline Lake, Livingston County - found in 2003 samples

  • The following lakes were found to not be infected by LMBV:

  • Lakeville Lake, Oakland County - sampled in 2002
  • Diamond Lake, Cass County - sampled in 2002
  • Wamplers Lake, Jackson County - sampled in 2002
  • Swains Lake, Jackson County - sampled in 2002
  • Union Lake, Branch County - sampled in 2002
  • Randall Lake, Branch County - sampled in 2002
  • Independence Lake, Washtenaw County - sampled in 2002
  • Eagle Lake, Van Buren County - sampled in 2002
  • Jordan Lake, Barry County - sampled in 2002
  • Norvell Lake, Jackson County - sampled in 2002
  • Nichols Lake, Newaygo County - sampled in 2003
  • Budd Lake, Clare County - sampled in 2003
  • Lake Nepessing, Genesee County - sampled in 2003
  • Clifford Lake, Montcalm County - sampled in 2003
  • Camp Lake, Kent County - sampled in 2003

The 2003 sampling by Michigan DNR Fisheries Division was more intensive and used more sensitive techniques than previous sampling. Disease detection improvements by fish health specialists lead by Dr. Mohamed Faisal at Michigan State University included the use of genetic and antibody testing that provided detailed data on the level of infection for individual fish within a given waterbody. Analysis of the results over the last 4 years have for the first time allowed the development of a disease model that allows fisheries biologists and health specialists to determine the stage of LMBV (early infection, peak infection and recovering) in a waterbody. Sampling will continue in 2004 and will include known infected lakes and additional northern lakes.

Michigan DNR Fish Production Manager Gary Whelan said LMBV appears to infect other fish species, including smallmouth bass, bluegill, and crappies, but has caused mortality to only largemouth bass. The disease typically kills large adult fish and die-offs impact approximately 10% of these fish in a given lake. Total losses in Michigan lakes have ranged from 100-500 adult fish per lake. A wide range in the percent of bass infected (from 6.3-100%) has been observed, with the highest infection rates in lakes with die-offs.

"The DNR cannot eradicate this virus or treat affected wild fish populations," Whelan said. "However, as we continue investigating this disease, we appreciate receiving reports of unusual fish mortalities." In 2002, many largemouth bass mortalities were reported during the mid-July to mid-August period and some of these were likely LMBV related. However, many of the reports came in weeks after the mortalities, which is too long for confirmation of the disease. In 2003, no large scale mortalities were reported which is likely from the mild summer weather conditions that reduced the stress on largemouth bass populations.

The disease usually causes mortality when fish are most stressed. Potential stressors include very hot weather, high angling pressure, and possibly aquatic weed or other treatments during very hot periods. Any measures that can be taken to minimize stress on these fish will reduce the impact of the disease and mortality.

There are few outward signs that a fish has the virus. The virus has been found in many lakes where there have not been reports of disease or mortalities of fish. Affected fish usually appear normal, although they may be lethargic, swim slowly, and are less responsive to activity around them.

Dying fish often are seen near the surface and have difficulty remaining upright. Upon internal examination, such fish usually will have bloated swim bladders, which accounts for the cause of swimming problems. Red sores or other lesions occasionally may be seen on the skin of the fish, but these are secondary in nature and not part of the virus infection.

Consistent with the recommendations reported from the Largemouth Bass Virus Workshops, sponsored by ESPN and BASS Federation, the DNR is calling on anglers who target largemouth bass to voluntarily help reduce angling stress on largemouth bass populations during warm weather. Acting DNR Fisheries Division Chief James Dexter noted the DNR will be monitoring lakes throughout Michigan this summer, in partnership with the Michigan BASS Federation.

"This is a new disease to northern lakes, and there is much for us to learn about how it works. For example, we still do not know how largemouth bass populations will be affected in Michigan's lakes in the long term," Dexter said. "We urge all members of the angling community to continue helping us monitor our waters. When you see unusually high mortalities of adult largemouth bass, please contact one of our offices immediately so we can investigate the die-off. Further, we look forward to working with our partners at the Michigan BASS Federation, and appreciate their willingness to assist us in collecting information necessary to better understand and manage this virus."

The DNR concurs with recommendations from the LMBV Workshops, and reminds anglers and boaters to take the following steps to help prevent the spread of the virus:

  • Clean boats, trailers, other equipment thoroughly between fishing trips to keep from transporting LMBV, as well as other undesirable pathogens and organisms, from one water body to another with special care to clean fishing equipment when you are done fishing known locations of the virus.
  • Do not move fish or fish parts from one body of water to another, and do not release live bait into any water body.
  • Handle bass as gently as possible if you intend to release them and release them as quickly as possible.
  • Refrain from hauling the fish for long periods in live wells if you intend to release them.
  • Minimize targeting of largemouth bass during the period from mid-July to mid-August, especially during exceptionally hot weather conditions.
  • Report dead or dying adult largemouth bass fish to Michigan Department of Natural Resources Fisheries Division offices.
  • Volunteer to help agencies collect bass for LMBV monitoring.
  • Educate other anglers about LMBV.

The Michigan DNR will continue to communicate any new information learned about the disease in Michigan.