January 2009
U.S. Water News Online
ROANOKE, Va. — Scientists looking for the cause of ongoing fish kills in several of Virginia's western mountain rivers haven't solved the mystery yet, but they may be getting close.
Tests of dying fish this year in the Shenandoah, upper James and Cowpasture rivers revealed the presence of a strain of bacteria that causes a disease with symptoms such as the cigar-burn like lesions found on the Virginia fish.
While the discovery of the bacteria Aeromonas salmonicida could be significant, it raises even more questions than scientists already were asking about the kills, said state Department of Environmental Quality biologist Don Kain.
For one thing, this type of bacteria is most commonly found in fish that inhabit cold northern waters, such as salmon or trout. Virginia has trout streams that run into the Shenandoah and James, Kain said, but no trout have died.
Most of the fish affected in Virginia were smallmouth bass or redbreast sunfish. Fish kills have been recorded over the past five years in the Shenandoah River and the past two in the James and Cowpasture, although the numbers were smaller this year.
Scientists found that the bacteria strain was present in the dying fish, but not in the water and not in fish before or after the kills. Scientists question could this bacteria, which causes a disease called furunculosis, be responsible for the kills?
"The answer is maybe,'' Kain said. "Right now there appears to be a strong association, which is not the same as cause and effect.'' One thing biologists working with a fish kill task force need to determine is whether the fish were already dying when they were infected by the bacteria.
"Is it something that showed up because the fish were weak, or is it something that made the fish weak?'' Kain said. The goal of tests next year, he said, will be to find out whether Aeromonas salmonicida is causing the kills, as well as how it's getting to fish in these rivers.
State scientists will seek help from a U.S. Geological Survey scientist who is familiar with the strain, Kain said. Dr. Rocco Cipriano, based in Leetown, W.Va., conducted bacterial analyses on fish from the rivers this year, a DEQ news release said.
This strain of bacteria cannot live in water above a temperature of about 77 degrees. The upper James, the Shenandoah and the Cowpasture typically are warmer than that during the summer, so Kain said the organism either may be living in feeder trout streams that stay cool or is being reintroduced into the rivers every spring.
That leads to the question of how it's getting into the fish. The strain could be carried by wildlife such as birds, Kain said, or in fishermen's bait buckets.
The transfer question also leads to another. Tests have shown no presence of the bacteria in fish in the Maury River, which lies between the Shenandoah and the James.
"Why would it skip over a river like that?'' Kain asked.
The poultry industry that dominates the agricultural Shenandoah Valley has received increased scrutiny since the unexplained kills began. But one task force finding — that other forms of aquatic life sensitive to toxic substances are healthy — appears to absolve agricultural runoff.
"We know, in these waters, if you look for chemicals you will find them,'' Kain said. But the fact that other aquatic life was unharmed, he said, "is reflective of productive, good water quality.''
However, factors indicate that fish in these rivers are under stress, even if it's not killing them.
Some fish are intersex — males with eggs. That condition can be caused by hormones, which have been found in treated sewage wastewater as well as poultry litter that is spread on farm fields as fertilizer.
Most of the task force's work has been funded by the state, so its budget next year may be tighter. The sour economy has prompted Gov. Timothy M. Kaine to call for budget cuts.
The discovery of the bacterial strain means the focus will be narrower, Kain said, so scientists should be able to work with a leaner budget.
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