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Largemouth Bass
Virus (LMBV) Fact Sheet
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 hatchery stock.
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 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.
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 fish.
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 Bass Virus?
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 new. Recent
evidence suggests that the virus was present during 1991 in Florida's
Lake Weir.
4. Where has Largemouth Bass
Virus been found?
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 for LMBV.
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 Michigan.
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 variability.
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 by LMBV.
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 and eat?
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 kills.
11. What can anglers do?
Anglers can help minimize the
spread of LMBV virus and its activation into a lethal disease
by doing the following:
--- 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
practice.
--- Never move fish or fish
parts from one body of water to another. And do not release live
bait into a fishery.
--- 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 wildlife agencies.
--- Volunteer to help agencies
collect bass for LMBV monitoring.
--- Educate other anglers about
LMBV.
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