Mar 11, 2001
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SPRINGFIELD, ILL. - As part of a nationwide protocol to test for and conduct research relating to largemouth bass virus (LMBV), Illinois has tested and found the virus at its hatcheries and several lakes in Illinois.

Results from the U.S. Fish and Wildlife Service LaCrosse Fish Health Center in LaCrosse, Wisconsin, and Auburn University, Auburn, Alabama, indicate the virus was found everywhere it was tested for in Illinois.

"Presence of the virus in a population does not mean the fish have disease, nor is it an indication that they will have the disease in the future," said Mike Conlin, IDNR Fisheries Chief. "Largemouth bass virus appears to be triggered by a combination of stress and heat. Fish are more likely to be impacted by the disease when they are stressed. Stress factors such as hot water temperatures, low oxygen, and frequent handling appear to increase the chances fish will show signs of illness."

Biologists noticed that the only fish in the hatcheries testing positive for the virus were under stressed conditions. They noted that when the primary cause of stress was removed, fish mortalities ceased or decreased dramatically.

Largemouth bass were tested from the Jake Wolf Hatchery, Little Grassy Hatchery, as well as four lakes with different variables. The lakes included Lou Yaeger, which experienced a multiple species fish kill this year and has not been stocked from the hatcheries; Jacksonville, which is routinely stocked and experienced a largemouth bass kill in August, likely caused by high temperatures and handling associated with a bass tournament; Crab Orchard, which is routinely stocked, receives heavy tournament pressure and had largemouth bass mortalities several years ago; and Cedar, which is not stocked, has only small local fishing tournaments and has had no reported bass kills.

2001 production fish from Little Grassy and Jake Wolf fish hatcheries, except those that were fin clipped for research purposes, were negative for the virus. IDNR is planning to stock the fish that tested negative in lakes around Illinois this fall.

LMBV first gained attention in 1995 when it was implicated in a fish die off in South Carolina. It is one of more than 100 naturally occurring viruses that affect fish but not warm-blooded animals. Although the virus can be carried by other fish species, such as crappie and bluegill, it is only fatal to largemouth bass. Scientists do not know exactly how the virus is transmitted or why it sometimes kills bass. Warm water temperatures is one common variable identified at lakes where LMBV related fish kills have been confirmed. Scientists know of no cure. LMBV has been found in at least 15 states. Generally, states that haven't reported finding it have not yet tested for the virus.

Most fish carrying LMBV appear completely normal. In cases where the virus has triggered disease, dying bass may be near the surface having difficulty swimming and remaining upright. LMBV attacks the swim bladder, causing bass to lose their equilibrium. Diseased fish might also appear bloated. Studies have shown that all sizes of bass may be carriers of the virus. However, larger bass are more apt to develop disease because they are more likely to undergo stress.

Although biologists do not know if the virus will have extensive or long-lasting effects on bass populations, Conlin does not believe it will harm fisheries in the long run. There have been no documented cases of LMBV kills in Illinois. In other states, bass populations in LMBV-infected lakes have not dropped significantly, though reductions in angler success have been noted subsequent to an incident for a year or two.

Fish with LMBV are safe to handle and eat. The virus does not infect warm-blooded animals, including humans.

Anglers can help minimize the impact of largemouth bass virus by doing the following:
- Drain all water from the bilge and live wells and clean boats, trailers, and other equipment thoroughly between fishing trips to prevent transporting
LMBV -- as well as other pathogens and organisms -- from one water body to another. The virus can live for several hours in water.
- Do not move fish or fish parts from one body of water to another. And do not release live bait into the water.
- Handle bass as gently as possible.
- Conduct tournaments during cooler weather, so fish caught will not be stressed by hot temperatures and low oxygen levels.
"Although the virus has been confirmed in only a handful of locations, the virus may be present elsewhere. In fact, results so far indicate we'll find the virus virtually anywhere we look for it," Conlin said.

If you see unusual numbers of dead or dying fish, call DNR's Law Enforcement Hotline at 1-877/236-7529, or contact a DNR fisheries biologist.
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