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Snakeheads: Teeth aren’t the only threat

Invasive snakehead fish in two Potomac River tributaries are carrying a virus that can kill largemouth bass, according to a new study by the U.S. Geological Survey and the Virginia Department of Game and Inland Fisheries.

The study, published in the Journal of Aquatic Animal Health, was co-authored by Luke Iwanowicz, a research biologist with USGS, and John Odenkirk, a fish biologist and snakehead researcher with the game department who works out of the agency’s Fredericksburg office.

The game department has been monitoring the spread of largemouth bass virus since it was first detected in Florida in 1991. The ranavirus can kill amphibians and is associated with significant population declines.

Infected bass can experience a loss of equilibrium, according to an article on the game department website, and float to the surface and die. Other fish species, such as sunfish, can harbor the virus, but only bass have developed a disease.

Testing for the virus in Virginia began in 2001, with only small pockets of it found in state waters. Tests in 2011 in 16 lakes and rivers found it was present in all. The new wrinkle is that it’s been found in the northern snakehead populations on Dogue and Little Hunting creeks along the Potomac River near Mount Vernon.

“It’s not good news, but the implications are not fully clear right now,” Odenkirk said Tuesday. “It might be a wash, or it might exacerbate the virus transmission.”

If it’s the latter, he says, it would be a concern because snakeheads are prolific in colonizing new areas and breeding.

“It’s a dispersal-minded fish.”

Odenkirk says there have been no reports of largemouth bass with symptoms of the virus found in the Potomac.

Iwanowicz says that the snakeheads, native to Asia, could be reservoirs of the virus, capable of transmitting it to largemouth bass in the Chesapeake Bay watershed.

The study says snakeheads examined from the Potomac were otherwise healthy, so it’s unknown whether the virus triggers the disease in them.

The Potomac River is a prime destination for bass anglers from spring through the fall. Since snakeheads—named for their shape and snakelike pattern on their skin—and bass populations overlap, it could foster the spread of the virus.

The game department has said infected bass are safe to eat and that the virus can’t be passed to humans. Snakeheads were first discovered in a Crofton, Md., pond in 2002, and in the Potomac River two years later.

“The long-term and population-level effects of largemouth bass virus on bass inhabiting these rivers are unknown,” Iwanowicz said in a press release.

How the virus is transmitted or activated is unknown, the study says. But genetic and other differences in the virus, stress from pollution, high water temperatures and other factors play into the disease in largemouth bass.

Rusty Dennen: 540/374-5431


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