What is Largemouth Bass Virus?

It is one of more than 100 naturally occurring viruses that affect fish but not warm-blooded animals. Origin is unknown, but it is related to a virus found in frogs and other amphibians and nearly identical to a virus isolated in fish imported to the U.S. for the aquarium trade. Although the virus apparently can be carried by other fish species, to date, it has produced disease (death) only in largemouth bass. Scientists do not know how the virus is transmitted or how it is activated into a fatal disease. In addition, they know of no cure or preventative, as is commonly the case with viruses.

LMBV first gained attention in 1995, when it was implicated in a fish kill on Santee-Cooper Reservoir in South Carolina. Since then, the virus has been found in impoundments throughout the South and, during 2000, was confirmed as the source of a kill in Lake George on the Indiana-Michigan border. Often, the virus has been detected in bass that show no signs of illness, which suggests that some fish might be infected but not ever become sick.

Some kills, however, have been linked to LMBV. Since all those die-offs occurred from June through September, warm-water temperatures might be a factor, particularly in southern fisheries, where surface temperatures can remain in the 90's for month at a time. No other common variables seem to exist among lakes where kills occurred. Some lakes, for example, contain aquatic vegetation and others do not, suggesting that herbicide management of aq1uatic plants did not trigger that disease to turn fatal.

Some scientists believe that "stressed" bass might be the most likely to die of the disease. Along with hot weather, stress factors might include poor water quality caused by pollution and frequent handling by anglers.

Thus far, LMBV-related kills have been minor in comparison to kills prompted by other causes, such as pollution. These largemouth bass die-offs have received considerable attention, however, because they involve the nation's most popular game fish.

No evidence presently exists that LMBV has caused a long-term problem on any fishery or that it will have a long-term impact.