VANCOUVER - Atlantic salmon farms around Vancouver Island have begun testing and formed a special outbreak management team after a virus outbreak at one farm led to a site quarantine and the cull of more than half a million fish.

The farm most seriously affected by the virus is one run by Mainstream Canada, which confirmed tests conducted earlier this week showed the presence of infectious haematopoietic necrosis at its site on the Island's west coast, located at Dixon Bay, north of Tofino, B.C.

A second farm announced Friday afternoon that the federal Department of Fisheries and Oceans has identified a "low positive result" for the same virus in coho salmon samples on a Sunshine Coast farm.

Grieg Seafood said further tests will be conducted next week.

Stewart Hawthorn, a spokesman for Grieg Seafood, said in a statement the low-positive test does not confirm the presence of the virus and additional tests will be conducted next week.

He said the test result is not entirely unexpected because the virus occurs in natural and wild salmon, and coho are local and wild.

Hawthorn said the company's fish are not showing any signs of disease or significant or unusual mortality, and out of caution Grieg is increasing its internal monitoring and implemented a voluntary isolation protocol.

Mary Ellen Walling, executive director of the BC Salmon Farmers Association, said an outbreak management team is now in place on Vancouver Island after the Mainstream incident and includes members from across the industry.

She said companies are ensuring heightened bio-security procedures are in place and are reviewing visitor, boat and plane traffic to farms and are now taking samples and testing for the virus on a priority basis.

"I don't think it's started yet on the east coast of the island but it will," she said. "The intention is that all of the farms will be tested."

Walling said the last few years have been challenging for the industry because of increased competition from Chilean farmed salmon in the U.S. market.

As a result, prices have dropped, she said, and B.C. remains the highest-cost producer in the world.

But she said the outbreak is expected to have little impact on the market because the virus does not cause any human-health concerns and demand remains high for B.C. product.

According to the Canadian Food Inspection Agency, the virus exists in B.C. coastal waters and does not affect human health or food safety, but it does pose a risk to aquatic animal health and the economy.

"We are taking samples at all our farm sites in Clayoquot Sound and on the east coast of Vancouver Island," said Laurie Jensen, a Mainstream spokeswoman. "This is a precautionary measure only. We want to know what's going on."

Mainstream Canada, which is headquartered in Oslo, Norway, is a subsidiary of Cermaq and also operates in Chile, Canada, Scotland and Vietnam.

The company produces 25,000 tonnes of fish in B.C. annually.

Jensen said she suspects the virus came from wild salmon, and the company has already begun to remove and cull about 560,000 Atlantic salmon, all less than a year old, from the Dixon Bay farm.

Just how much the cull will cost the company is not yet known and won't be known, said Jensen, until the farm has been depopulated and disinfected.

Equipment, like nets, that can't be disinfected will have to be destroyed, too, said Jensen.

She expected the depopulation and cull to have a significant impact, adding the company will probably leave the farm to fallow, without restocking, for at least three to four months.

"Right now, this is not about he cost. This is about the fish. We want to keep the fish surrounding the area healthy, we want to keep the oceans healthy, we want to, as humanely as possible, remove these fish," she said.

The company is taking the outbreak seriously because it doesn't want to see the virus spread, but it doesn't foresee any layoffs in the future, said Jensen.

She said the company operates about 14 sites in Clayoquot Sound, employing about 150 people in the communities of Ahousaht, Tofino, Ucluelet and Port Alberni.

Todd Waterfield, president of Lions Gate Fisheries Ltd, a fish wholesaler, said when ready for market, Atlantic salmon fetch a wholesale prince ranging from $5.72 to about $7 per kilogram.

"They don't really fluctuate a lot," he said, noting prices have been pretty steady in the last few weeks.

But he said he doesn't know what the culled fish would be worth because he doesn't know how much it would have cost to grow them.

According to B.C.'s Ministry of Environment, the province's salmon farming industry is the fourth largest producer of farmed salmon in the world, and in 2009, 18 companies operated on 131 sites.

The ministry says the value of Atlantic farmed salmon was estimated at $470.3 million in 2010.