Virus Kills Swaths of Fish in Great Lakes

Canadian researchers are monitoring fish farms and hatcheries in Ontario for signs of a deadly virus suspected of killing tens of thousands of fish in the Great Lakes basin in recent months.

The virus is called virus haemorrhagic septicaemia (VHS) and it causes fatal anaemia and haemorrhaging in various fish species. Although it does not pose a human health risk, the mortality rate in fish is up to 80 percent, according to he Disease-Watch website.

The VHS outbreak first came to the attention of the Ministry of Natural Resources this Spring when roughly 30,000 dead fish washed up on the shores of Lake Ontario. Tissue samples from the fish later tested positive for VHS.

Although the virus has only been found in the wild so far, experts are concerned that the disease will spread to Lake Ontario's fish farms and hatcheries since the infection is easily transmitted. According to the World Organization for Animal Health, VHS infection can occur across species and is spread via contaminated water or by direct contact with urine, sexual fluids, or the gills and skin of infected fish. Moreover, the virus can be carried downstream as far as 10 - 20km.

"Our concern is pretty high, especially for some of our farms that grow in cages in the open waters of the great Lakes," University of Guelph professor Rich Moccia told the Globe and Mail . "They come into contact with wild fish that are the initial carriers… so we may see the virus developing in farms."

It is not known where the virus came from or how fast it could spread. Prior to 1988, the virus had only appeared in Europe, mostly in rainbow trout fish farms. North America's first case occurred in 1988 in spawning salmon in the American Pacific Northwest. Up until 2003, the virus appeared to be confined to saltwater species in populations off both coasts. In 2005, however, VHS was detected in muskellunge in Michigan's Lake St. Claire and in Lake Ontario, according to Department of Natural Resources (DNR) reports.

Finally, in May this year, massive fish die-offs due to VHS occurred in the St. Lawrence River and Lake Ontario's Irondequoit Bay near Rochester, New York.

It is too early to tell what the impacts might be on fish farmers and the aquaculture industry in the Great lakes. However, outbreaks in Europe had considerable negative impacts on the ecology and economy. A U.S. Geological Survey report estimated that VHS infection had caused more than $40 million USD in annual losses at rainbow trout farms in Europe prior to 1989.

There are no large-scale treatment measures for VHS outbreaks occurring in the wild. However, the disease's spread may be limited by not transferring fish between bodies of water, and thoroughly cleaning boats trailers, nets, and other equipment when traveling between different lakes and streams.

The National Aquatic Animal Health Program recommends reporting fish with suspicious signs and symptoms to local fisheries or Fisheries and Oceans Canada (FOC).