"LMBV prevalence has declined and maybe LMBV is gone or going away," said Mike Maceina, a fisheries professor from Auburn University.
In speaking at the fifth annual gathering, Maceina was referring specifically to findings from fieldwork conducted at Alabama reservoirs. But his words accurately reflected the generally optimistic tone of the Feb. 27 meeting, which was attended by resource managers and scientists from across the country.
State biologists reported only two minor kills linked to LMBV during 2003, at Lake Wes Watkins in Oklahoma and Lake Paho in Missouri. Fieldwork, meanwhile, revealed that fisheries once damaged by kills continue to rebound, and research confirmed that warm water and crowding contribute to the prevalence and transmission of the virus.
"Altogether, we've had five kills and 23 of 55 lakes tested positive," said Dave Terre, regional director for Texas Parks and Wildlife. "But we've had no kills recently, and Fork and Rayburn have rebounded tremendously."
In Alabama, Maceina's team worked with tournaments to look at bass populations in Wheeler, Eufaula, and other fisheries.
"At Wheeler, the virus was first detected in 1997," he said. "Then we lost the big fish in 1999 and 2000."
While LMBV is noted to be a killer of large bass when it turns deadly, scientists found the highest prevalence of the virus in bass 12 to 15 inches long. "You just don't see it in bass over 20 inches," Maceina said.
Those infected smaller fish experience slower growth rates and that, combined with a die-off of big bass, explains why anglers report more difficulty catching fish of 5 pounds or larger following an LMBV-related kill, the scientist explained.
"A decline in big fish is due to slower growth and lower survival," he said. "The good news is that, by 2003, growth and survival rates had improved in most Alabama reservoirs."
And by implication, that is good news for other fisheries damaged by LMBV, from Texas to Michigan.
Maceina also confirmed what biologists have long believed regarding the role that stress and warm water play in LMBV outbreaks. "Holding fish for two to five days seems to increase the prevalence of the virus," he said. "And higher temperatures do, too."
In the laboratory at the University of Illinois, professor Tony Goldberg discovered "a slight tendency for crowded fish to have higher viral loads.
"The difference (between being crowded and not crowded) is small, but statistically significant," he said.
During 2002, Goldberg and his associates found that LMBV-infected fish died more quickly at 30 degrees Centigrade (87 Fahrenheit) than at 25 degrees Centigrade (77 Fahrenheit).
"The virus replicates more efficiently at that temperature," he said. "And it's important to remember that we're working with northern largemouth bass in Illinois. The thermal optima may be different in different places."
Goldberg rated elevated water temperature as a high risk factor, with crowding, direct contact, and water-quality change as medium risks.
"Expect kills when water quality changes rapidly or fish are crowded," he said. "Catch-and-release angling is okay (during hot weather), but do not subject fish to elevated temperatures and crowded conditions."
To simulate stress from angling, Goldberg's team attached fishing line to small tank-held bass infected with LMBV and "played them."
"The angling event made no difference in survival," he said. "Temperature, not angling, alters susceptibility."
At least in the laboratory, he noted.
"We need more field studies to help determine how these factors (angling, crowding, temperature) affect fish in complex ecosystems," added Goldberg.
At the Warm Springs Fish Health Center, scientists were unable to isolate live virus from the feces of herons and cormorants. That suggests that fish-eating birds do not spread LMBV.
They also found that LMBV is a tough and hardy virus, surviving both temperature changes and drying. Just allowing a livewell to dry for two or three days, in fact, likely is not enough to keep an angler from transporting the virus from one fishery to another. Researchers suggest thoroughly bleaching, then thoroughly rinsing, livewells between visits to different bodies of water.
Throughout this past year's research, scientists continued to refine and improve their methods of checking bass for LMBV.
Finding a quick and non-lethal way of testing, however, remains a research priority. Others include further examination of LMBV's long-term effects on fisheries populations and investigating a possible connection between the virus and bacterial infections. Scientists also want to trace the virus' movement through infected fish and try to determine why LMBV kills some fish and not others. And they want to find out how long antibodies remain in previously infected fish.
Those attending this fifth annual meeting agreed that, overall, resources managers are in "monitoring mode" and that LMBV now seems to pose far less of a threat than it did in 1998 and 1999.
Nevertheless, they will remain ever vigilant.
"Sub-lethal effects are of concern to me," said Louisiana's Mike Wood, a state fisheries biologist. "Maybe we have problems that we haven't recognized yet."
Oklahoma's Gene Gilliland, a senior fisheries biologist for the Oklahoma Department of Wildlife Conservation added, "What's going to happen 10 or 15 years from now is of concern to all of us."
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FACT SHEET
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.
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