Largemouth Bass Virus Workshop V, sponsored by BASS
1. What is Largemouth Bass Virus (LMBV)?
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 United States for the aquarium trade. Although the virus apparently can be carried by other fish species, to date, it has produced disease only in largemouth bass. The virus is spread through contact with other infected fish or contaminated water. However, scientists still do not know why it causes disease in some fish and not others. 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, north as far as Vermont, and south into Florida.
During 2000, LMBV was implicated 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.
During 2002, the virus was reportedly detected in Lake Michigan and at Lake Champlain in Vermont.
Often, LMBV has been found in bass that show no signs of disease, which suggests that some fish might be infected but never become ill.
Some kills, however, have been linked to LMBV. Since all those die-offs occurred from June through September, warm-water temperatures likely are a factor, particularly in southern fisheries, where surface temperatures can remain in the 90s for months at a time. Research in 2002 and 2003, in fact, documented that belief, as infected fish in tanks died 3.3 times faster at 30 degrees Centigrade (86 degrees Fahrenheit) as they did at 25 C (77 F).
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 other pathogens, poor water quality caused by pollution, crowding in livewells and tanks, and frequent handling by anglers.
Thus far, LMBV-related kills appear to be 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, and it is unclear whether it will have a long-term impact. But scientists are investigating how the virus might affect behavior, reproduction, and growth rates of bass, particularly younger fish. During 2003, researchers in Alabama determined that fish infected with LMBV require three to four years longer to reach 5 pounds than do their healthy counterparts.
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 may 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 buoyancy control. Diseased fish might also appear bloated.
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 believe 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 19 states: Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Michigan, Missouri, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, Vermont, and Wisconsin.
From 1998 through 2003, the U.S. Fish and Wildlife Service, state wildlife agencies, and university labs sampled fish at 494 sites. LMBV was found at 208 locations. Fish kills attributed to LMBV have occurred in more than two-dozen locations. Since 2001, however, kills have been infrequent and minor. During 2003, minor kills occurred at Lake Paho in Missouri and Lake Wes Watkins in Oklahoma.
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.
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 proven 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, Suwannee 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, Illinois at Urbana-Champaign, Louisiana State, Mississippi, Mississippi State, and Texas A&M. The federal Sport Fish Restoration Program, also known as Wallop-Breaux, has provided funding for this work.
Researchers still are looking to perfect non-lethal sampling methods. They also want to investigate further LMBV's long-term effects on fisheries and its chronic/sub-lethal effects on bass. They want to explore possible connections between LMBV and bacterial infections, and they want to track the virus' movement through infected fish.
10. What the experts think:
With so little known about LMBV, scientists still are making new discoveries. 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 impose added pressures on bass populations.
11. What can anglers do?
Anglers can help minimize the spread of LMBV and its activation into a lethal disease by doing the following:
-- Thoroughly clean livewells, boats, trailers, and other equipment between fishing trips to keep from transporting LMBV - as well as other undesirable pathogens and organisms - from one water body to another. A good treatment for livewells is 1/4 cup of chlorine bleach per gallon of water. Make sure that contact time with bleach is at least 5 minutes. Rinse thoroughly after bleaching. Research has determined that the virus can live for several hours in water, but that bleaching kills it. Also, scientists recently learned that several strains of LMBV exist, with some more deadly than others, thus confirming even more the importance of these precautions.
-- Do not 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 weigh-in tournaments during cooler weather, so fish caught will not be so stressed. Utilize "paper" tournaments during hot weather, with anglers measuring fish and immediately releasing them.
-- Report dead or dying fish to state wildlife agencies.
-- Volunteer to help agencies collect bass for LMBV monitoring.
-- Educate other anglers about LMBV.