LARGEMOUTH BASS VIRUS UPDATE

    In Central Florida’s Lake Weir, what has come to be known as the Largemouth Bass Virus (LMBv) was discovered in 1991.  Four years later, in Cooper Reservoir, South Carolina, the first related incident of fish mortality was reported, and the virus proved itself to be one worthy of state department attention.

    In 2001, the Virginia Department of Game and Inland Fisheries first tested impoundments for the presence of LMBv, many showing no signs of infection or otherwise low exposure rates; but the virus’s presence was nonetheless realized in Virginia.

    Because LMBv is a potential threat to America’s favorite game fish, panic and dismay surrounded the initial discovery.  However, the course of the disease, as studied in southern waters, supports biologists’ assurances that LMBv poses a relatively insignificant effect on infected fisheries.

    Fishermen first noticed only a decrease in the catch rate of quality fish—defined as being three pounds and larger—as a result of a decrease in fry survival and growth rates.  Now, 12 years since the initial discovery, it seems the worst has passed, and some of the early detection sites are returning to post-infection fishing conditions.

    Testing resumed in Virginia waters in the summer of 2010.  Of the three impoundments tested, all returned positive for the virus, and two replied with notably significant exposure rates—Kerr Reservoir (Buggs Island) showing 41% exposure, and Briery Creek Lake showing 30%--both of which also tested positive in 2001.  Both “big fish” fisheries, Buggs and Briery became the martyrs for the cause.

    A year later, 16 bodies of water were tested across the state, ranging from small, department-owned lakes to large impoundments and major rivers.  All locations showed signs of infection, save for the tidal James River.  From this, VDGIF fisheries biologist Dan Michaelson can infer that “LMBv will probably be found in most of the water bodies in Virginia.  Some will be impacted by the disease and others may never show indications that the fish have been exposed.”

    There is a silver lining, however.  In the 2011 tests, Briery Creek and Buggs Island showed exposure rates of 30% and 23%, respectively, indicating that, as compared to results from 2010, the virus in those fisheries has surpassed its peak of potency, and is now on the decline.

    According to Dan Michaelson, “the southern states that experienced this outbreak in the late 1990s showed about a 3-year recovery cycle after LMBv was detected.  Considering Virginia’s cooler temperatures and slower growth rate, he speculates that “the cycle will be about five years in Virginia.”

    For those fish that do survive the initial exposure, immunity can be developed.  “Unfortunately, they do not pass the resistance on to their progeny,” says Michaelson.  However, the good news is that states that met the virus early on, like Texas, Mississippi, and Florida, no longer observe noticeable impacts of the disease.  Most biologists predict that in Virginia, too, LMBv will become little more than a means of population control, similar to old age.

    As for what causes the virus to emerge, biologists again claim little knowledge.  Outbreaks and the few small mortality events that have occurred are most frequent in the warmer months of the year due to stress that may be linked to low oxygen levels, high water temperatures, and increased tournament pressure. 

    Effected fish usually show no signs of the virus, but may suffer from loss of equilibrium or the inability to stay below the surface due to an over-inflation of the swim bladder.

    But despite the large presence of LMBv in Virginia, most of the infected areas still maintain exceptional angling opportunities for the angler, which will only increase in status as the virus runs its course and shrinks into the background of biological issues.

    Still, it is important to help stop the spread of the virus which, as it is not known exactly what causes an outbreak, includes a wide range of responsible practices.  Using common sense boat hygiene, like cleaning trailers and not emptying water from a livewell into a foreign water body, is an effective measure for stopping the spread of both LMBv and invasive species.  Also, it is encouraged to limit the practice of bass tournaments in the hottest months of the year, and to handle fish delicately and briefly.  To help prevent the spread of the disease and other biological issues, the transplantation of fish into foreign impoundments is discouraged.  More information concerning preventative measures can be found on the Department’s website.

    Considering the facts, LMBv carries little long-term threat for Virginia’s bass anglers, and the end of the tunnel is in sight.  Biologists continue to monitor bass fisheries and educate anglers to help stop the spread of the disease.  Michaelson assures anglers, “we fully expect all of these fisheries to recover.”  There is no cause for concern. 

*Originally published in the Rural Virginian