A fisheries scientist was accused at a federal inquiry of deliberately avoiding research into the impact of fish farms on wild salmon, even though that should have been part of his job.

But Michael Kent, an Oregon State University microbiologist and former employee of the Department of Fisheries and Oceans vigorously defended himself, saying he didn't find much evidence of diseases being transferred to sockeye salmon from fish farms.

The testy exchange between Kent and Gregory McDade, a lawyer for a coalition of anti-fish farm activists, marked testimony at the Cohen Commission on Tuesday, which this week began some of its most controversial hearings.

Federal fisheries officials also confirmed they had assigned a security guard to Kristi Miller, head of molecular genetics at DFO, who attended the inquiry with her husband and the guard Tuesday afternoon. She is scheduled to testify Wednesday.

Melanie McNabb, a DFO spokesperson, said while there was no specific threat to Miller, the commission itself had raised its own security.

The Cohen Commission was called into the 2009 collapse of the Fraser River sockeye salmon stocks and has been holding months of hearings, mostly in obscurity.

But for the next two weeks, Commissioner Bruce Cohen, the B.C. Supreme Court justice who is leading the inquiry, is hearing testimony about fish diseases and fish farms.

McDade demanded Kent explain why the scientist didn't include information in his report to the commission about the transmission of sea lice from open net-cage salmon farms to wild salmon stocks, specifically sockeye.

"The question I'm asking you is whether your report didn't cover the problems from fish farms, regardless of the reason why," said McDade, lawyer for the Aquaculture Coalition.

"That's correct," said Kent.

""It didn't, did it?" asked McDade again.

"It did not cover, when I talk about each particular disease and its role ... I do not include a section saying what the risk of the disease is emerging from fish farms," said Kent.

"In each particular disease I did not talk about what the role of fish farms would be in transmitting to sockeye salmon."

At one point, McDade charged that Kent was a disease expert who was contracted to deal with such questions and that he consciously ignored the issue of diseases and salmon farms.

But Kent said other experts, specifically those from the industry, would deal with the matter in their reports.

He also said he did not find "great evidence of diseases being transferred from fish farms" when it came to the issue of sockeye salmon.

Later, a lawyer for a collection of environmental groups tried to turn the debate about the threat to wild salmon from fish farms on its head.

Tim Leadem, who is the Conservation Coalition, suggested the farmed fish are actually at risk of disease from wild fish. Government and industry could protect fish farms from diseases by moving the farms, he argued.

Those who oppose fish farms have long argued they should be moved to closed tanks on land.

Brenda Gaertner, lawyer for 12 B.C. First Nations, asked Dr. Stewart Johnson, head of aquatic animal health at DFO, if federal fisheries officials could protect migrating salmon stocks from diseases by moving salmon farms.

Stewart agreed, saying that would help if pathogens were being shed by salmon farms.

Gaertner repeated her question.

"If in the meantime we wanted to protect wild stocks from being exposed to pathogens, what human behaviour can we do? We could move net farms, is that agreed?"

"It's one thing that I guess you could do, yes," answered Stewart.