....fish-killing disease in Lake Erie

[Spiel]

Whatever happened to . . . . fish-killing disease in Lake Erie appears not to be spreading beyond Great Lakes watershed

 

 

September 01, 2008

John Mangels / The Plain Dealer

 

 

What is the status of viral hemorrhagic septicemia, a fish-killing disease that wiped out thousands of Lake Erie yellow perch, drum and walleye in 2006?

 

The virus is still out there, although for now it appears not to have spread much beyond the Great Lakes watershed.

 

Viral hemorrhagic septicemia, or VHS, is a contagious illness that kills a variety of fresh- and saltwater fish.

 

As its name implies, the disease causes bleeding - in the eyes, skin, gills and at the base of fins.

 

Fortunately, VHS doesn't sicken people. The virus can't survive in warm-blooded animals. But it poses a big threat to the commercial and sport fishing industries.

 

European countries have struggled with VHS for years, but before 2003, the only North American fish known to be infected were ocean-dwelling fin fish.

 

Then, beginning in 2005, large fish-kills occurred in several areas of the lower Great Lakes, including Lake Erie. Tests showed the culprit was VHS, and that it had been present in Lake St. Clair - which lies between Lake Huron and Lake Erie - as long ago as 2003.

 

How VHS got into the Great Lakes is a mystery. An ocean-going ship could have dumped infected ballast water while traveling one of the lakes. Or it's possible the viral strain that had been killing saltwater fish mutated into a form that is deadly to native freshwater species.

 

Concerned about the possibility that VHS might spread to other parts of the country, federal officials in October 2006 banned the interstate transport of 37 species of live fish caught in the eight states bordering the Great Lakes. The restrictions have since been loosened somewhat, but the order remains in place.

 

State and federal officials recently tested more than 4,200 VHS-susceptible fish collected last fall, and this spring from 22 Ohio lakes, rivers and reservoirs. They found no evidence of the virus in any of the fish, but they aren't ready to celebrate.

 

"I think it's too early to be able to say" what the results mean, said Jill Rolland, assistant director of U.S. agriculture department's aquaculture, swine, equine and poultry programs. "I think we're in the early stages of trying to understand ecologically what's going on with this."

 

One possibility, according to Ohio Sea Grant fisheries biologist Eugene Braig, is that after a few seasons of large die-offs, wild fish populations gradually build up immunity to VHS and the virus "just becomes part of the background."

 

"You want to slow its spread as much as possible," Braig said, "and you especially don't want it to get into culture operations" such as fish farms, where the economic impact could be devastating. But the biologist said he is "skeptical regarding the long-term impact of VHS on large wild fish populations."

 

Rolland cautions, though, that eventual immunity to a virus isn't necessarily assured. "That's the best-case scenario," she said. "There are other cases where, with each successive generation, that immunity isn't passed along to the juveniles and you go through the whole process again of being exposed and becoming infected and experiencing die-offs."