Largemouth Bass Virus (LMBV)
1. 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 is carried
by other fish species, to date, it has produced disease only
in largemouth bass. Scientists do not know how the virus is transmitted
or how it is activated into 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 lakes
and impoundments from Texas east to the Chesapeake Bay area and
south into Florida.
During 2000, LMBV was confirmed as the
source of a kill in Lake George on the Indiana-Michigan border.
The following year, minor kills were attributable to LMBV in
the same general area, with the virus being found in two lakes
in Michigan, three in Indiana, and two on the border. Illinois
also reported finding the virus in fish from four lakes and in
Often, LMBV has been found in bass that
show no signs of disease, which suggests that some fish might
be infected but not ever become ill.
Some kills, however, have been linked to
LMBV. Since all those die-offs occurred from June through September,
warmwater temperatures might be a factor, particularly in Southern
fisheries, where surface temperatures can remain in the 90s for
months 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 aquatic plants did not trigger the disease to turn
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.
Thus far, LMBV-related kills have been
minor in comparison to kills prompted by other causes, such as
pollution. These incidents have received considerable attention,
however, because they involve the nation's most popular game
No evidence exists that LMBV has caused
a long-term problem on any fishery or will have a long-term impact.
But scientists are investigating how the virus might affect growth
rates of bass, particularly younger fish.
2. What are the signs of Largemouth
Most bass infected with LMBV will appear
completely normal. In those cases where the virus has triggered
disease, however, dying fish will be near the surface and have
trouble swimming and remaining upright. That's because LMBV appears
to attack the swim
bladder, causing bass to lose their balance.
Diseased fish might also appear bloated.
The occurrence of lesions or black spots
is not necessarily a symptom of LMBV.
Adult bass of two pounds and more seem
to be the most susceptible to disease.
3. Is Largemouth Bass Virus a new disease?
No one knows. Because LMBV has been confirmed
in so many places at nearly the same time, some scientists suspect
the virus has been around for a while. Others suggest that "genetic
sequencing information" indicates that it may be relatively
evidence suggests that the virus was present during 1991 in Florida's
4. Where has Largemouth Bass Virus been
Since 1995, LMBV has been found in 17 states:
Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky,
Louisiana, Michigan, Missouri, Mississippi, North Carolina, Oklahoma,
South Carolina, Tennessee, Texas, and Virginia. Other states
have monitored for the virus, but did not find it. Others plan
to do so in 2002. Between March and November 2000, researchers
examined 3,476 largemouth bass and related sunfish species in
nine southeastern states, according to the federal Warm Springs
Fish Health Center. Of those, 464, or 13 percent, tested positive
Fish kills attributable to LMBV have been
confirmed in more than two dozen locations. During 2001, however,
mortalities reported were the lowest in several years. Minor
kills occurred in Arkansas, Georgia, Indiana, Louisiana, and
Additionally, the presence of the virus
itself seemed to decline in Southern waters. In Texas, for example,
only 45 of 899 adult-size largemouth bass sampled in LMBV-positive
reservoirs were infected. Previously, infection rates in some
fisheries were more than 50 percent of sampled bass.
5. What are the impacts to bass populations?
Scientists do not know enough yet about
the virus to determine if it will have long-lasting effects on
bass populations. Indications are, however, that it will not
harm fisheries long-term. Surveys on lakes following a kill suggest
that fish populations remain within the normal range of sampling
6. What are the impacts to fishing?
Following some kills, anglers have reported
catching fewer bass, especially bigger fish. But indications
are that an infected fishery will recover within a year or two.
More largemouth bass are killed annually
by other known diseases or poor environmental conditions than
7. Are other fish and animals affected
by Largemouth Bass Virus?
LMBV is a virus of the type that affects
only cold-blooded animals. Researchers have found it in other
centrarchids, but, thus far, it has proved to be a fatal disease
only for largemouth bass. Other members of the sunfish family
found infected with the virus include smallmouth bass, spotted
bass, Suwanee bass, bluegill, redbreast sunfish, white crappie,
and black crappie.
Amphibians, reptiles, and other fish species
could be carriers of LMBV. Scientists have found LMBV to be 98
percent identical to a virus found in guppies and "doctor
fish," a freshwater aquarium species imported from Southeast
Asia. This suggests that LMBV could have originated with importation
of an exotic species.
8. Are infected fish safe to handle
Yes. LMBV is not known to infect any warm-blooded
animals, including humans. But common sense should prevail at
all times: Thoroughly cook fish that you intend to eat. Also,
fish that are dead or dying should not be used for human food,
regardless of the cause of the illness.
9. What can and is being done.
As with many fish viruses, little is known
about LMBV. But because of the popularity of largemouth bass,
state and federal agencies, universities, and private-interest
groups are working hard to learn more about the virus and its
impact on the resource. Universities involved with LMBV include
Arkansas-Pine Bluff, Auburn, California-Davis, University of
Illinois, Louisiana State, Mississippi, Mississippi State, and
Texas A&M. During 2001, the federal Sport Fish Restoration
Program, also known as
Wallop-Breaux, provided more than $400,000 for LMBV research.
10. What the experts think.
Because so little is known about LMBV,
scientists have few conclusions to offer regarding the virus.
They do suggest, though, that LMBV probably will become an enduring
element in ecosystems and a component in natural selection. In
other words, it could serve as a population control. On the positive
side, scientists believe that LMBV does not appear to have the
potential to cause anything more than minor and sporadic fish
11. What can anglers do?
Anglers can help minimize the spread of
LMBV virus and its activation into a lethal disease by doing
--- Clean boats, trailers, and 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. Recent research has determined that
the virus can live
for several hours in water, confirming the importance of this
--- Never move fish or fish parts from
one body of water to another. And do not release live bait into
--- Handle bass as gently a possible if
you intend to release them.
--- Stage tournaments during cooler weather,
so fish caught will not be so stressed.
--- Report dead or dying fish to state
--- Volunteer to help agencies collect
bass for LMBV monitoring.
--- Educate other anglers about LMBV.
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