PITTSBURGH -- Since late-August thousands of fish have washed up on the shores of Pymatuning Reservoir. The fish kill, described as "significant," has impacted just one species, the common carp.
Last week a Minnesota testing lab confirmed what biologists from the state Fish and Boat Commission had suspected. The cause is koi herpes virus, a disease that since the 1990s has killed fish in the carp family in Europe, Asia, the Middle East and North America.
"Wherever it hits, it hits a large number of carp," said Tim Wilson, a biologist with the state Fish and Boat Commission. "In the United States it's hitting, checkerboarding, all over the place."
KHV is a carp-specific virus that cannot be contracted by humans or other fish species. It is spread fish-to-fish, secreted through the skin and waste. Wilson said that because most carp are bottom feeders, the virus may also be transmitted orally.
The washups have occurred in Ohio and Pennsylvania jurisdictions of the co-managed impoundment. Dan Bickel, manager of Pymatuning State Park in Pennsylvania, said none of the dead fish were found near the spillway, a popular tourist attraction where visitors toss bread to mooching carp numbering in the thousands -- so many that gulls can walk across the carp without touching the water. Wilson said the virus had not spread to sanctuary waters on the north end of the lake.
"Fortunately we're seeing fewer fish washing up in the last week, and as the lake cools we'll see even less," he said.
Researchers aren't sure why but recent studies showed that KHV kills carp only when the water temperature is between 64.4 degrees and 82.4 degrees.
"Above or below that the fish can survive," Wilson said. "I believe any fish that survives can develop an immune response. Next year the carp population will be down significantly -- the hope is any that survive will have developed that immunity."
The standard statewide fish consumption advisory for recreationally taken sport fish, one meal or one-half pound per week, has not been increased for fish caught at Pymatuning Reservoir. Wilson said dead carp continue to be collected for more testing at University of Minnesota's Aquatic Invasive Species Research Center and other labs.
Since August, as many as 1,000 white-tailed deer may have died from a viral disease that has spread through southwestern Pennsylvania. The state Game Commission is monitoring the spread of epizootic hemorrhagic disease in parts of Allegheny, Beaver, Butler, Lawrence and Washington counties.