Great Lakes Fish Virus May Threaten U.S. Aquaculture
CHICAGO -- A virus in the U.S. Great Lakes that has killed tens of thousands of fish in recent years is spreading and poses a threat to inland fish farming, a U.S. Agriculture Department official said Monday.
The pathogen, viral hemorrhagic septicemia, or VHS, causes internal bleeding in fish. It does not harm humans, even if they eat infected fish.
The federal agency issued an emergency order in October to limit movement of live fish caught in the eight states bordering the Great Lakes and two Canadian provinces.
"We're concerned that this virus could get out of the Great Lakes and affect other populations," Jill Roland, a fish pathologist and assistant director for aquaculture for the USDA in Riverdale, Maryland, said in a telephone interview.
"The virus could potentially affect the catfish industry," she said.
Catfish make up the largest sector of the $1 billion U.S. aquaculture industry, accounting for $462 million in sales, according to a 2005 USDA aquaculture census.
The public first began hearing about the virus after a die-off of fish in Lake Ontario, Lake Erie and the upper St. Lawrence River in May 2006 with dead fish washing up on beaches.
There is little the government can do to prevent the spread of the disease, other than limiting human movement of fish that may have the virus.
Fish caught in the Great Lakes may be used as bait in other parts of the country, with extra fish dumped into the water. Commercial farms sometimes get their breeding stock from wild fish.
However, fish migrate naturally and the Great Lakes does connect with the Mississippi River, a major waterway that runs to the Gulf of Mexico.
Scientists believe the VHS virus has been in the Great Lakes since 2003. Its origin is unknown but researchers think it may have come from bilge water released from one or more of the hundreds of ocean-going vessels plying the Lakes.
Another strain of the virus has affected trout and other freshwater fish raised commercially in Europe for several years.
"It has caused huge problems," said Roland of the virus in Europe.
Scientists are not sure how easily the virus is transmitted between fish and what percentage of infected fish develop symptoms and die. Fish can also be infected by water contaminated with the virus.
"We're not quite sure just how deadly to fish it's going to be yet," said John Dettmers, senior fishery biologist at the Great Lakes Fishery Commission in Michigan. "There are 37 susceptible species so far that we are aware of."
Those species include lake whitefish, walleye and yellow perch, all among the top commercially fished species in the Great Lakes, Dettmers said.
Symptoms can include bulging eyes, bloated abdomens and lesions that look similar to other diseases, so testing is necessary to confirm VHS is the cause.
The virus has been detected in three of the five Great Lakes -- Huron, Ontario and Erie. It will probably eventually spread to lakes Michigan and Superior, Dettmers said.