Bacterial disease killing striped bass

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By Steve Szkotak ASSOCIATED PRESS

RICHMOND | A chronic bacterial disease that infects more than half of all the striped bass in the Chesapeake Bay is also lethal to the prized game fish, researchers concluded.

Scientists at the Virginia Institute of Marine Science (VIMS) said they are the first to conclusively link mycobacteriosis to the death of rockfish, the more common name for the Bay's stripers.

Although the disease was first detected among Bay rockfish in 1977, its virulence was not immediately apparent because the fish were not dying in large numbers.

"They're just going to drop out of the population one by one," David Gauthier, lead author of the study, said of the infected stripers. "It takes a long time to kill a fish."

The study appears in the October issue of the journal Ecological Applications. It was conducted by researchers at VIMS, based in Gloucester Point, and from Coastal Carolina University and the U.S. Geological Survey's National Wildlife Center.

Mycobacteriosis slowly eats away at a fish's scales, scarring its streamlined, silvery body. The disease is usually harmless to humans, provided they wash their hands after handling infected fish.

Handling an infected fish with an open wound could cause lesions.

"It's a common-sense thing," Mr. Gauthier said. "It's a really good idea to wear gloves."

Infected fish also are safe to eat, but should be cooked thoroughly, he said.

While up to 60 percent of striped bass in the Bay are now afflicted, older fish are infected at higher rates. The estuary is the primary East Coast destination for striped bass to spawn. The game fish is coveted along the East Coast and is often on the menus of high-end restaurants.

It is not clear how mycobacteriosis spreads, nor why the disease has increased sharply in recent years. The disease, however, has historically been found among farmed fish.

"What makes it unique is you don't see it prevalent in a wild population," said Mr. Gauthier, who is an assistant professor in Old Dominion University's department of biological services.

He said the bacterial infection is a "stress disease," and he cited several theories on what is causing it among the bay's stripers.

They include the Bay's low-oxygen "dead zones," which could be forcing rockfish out of their preferred cold water into warmer waters, and low food supplies.

The study found a higher mortality rate in the summer months.

The mycobacteriosis-death link is based on fishery stock assessments that show an increase in natural deaths among striped bass in Maryland waters since 1999.

The scientists used 1,420 stripers in their sample and determined each fish's age, sex and whether it had mycobacteriosis. They then used a mathematical formula to conclude whether the stripers were dying from the disease or from other causes.

Among other findings, the scientists found that older females are more likely than males to die from the disease, a likely toll of spawning and migration.