Salmon exposed to a deadly virus pose no risk for Canadian exports being sold to the United States, the Canadian Food Inspection Agency said during a news conference Friday.

The CFIA has been criticized for its decision to allow about 240,000 salmon that had been exposed to infectious salmon anemia (ISA) to grow to market size in open-sea cages near Shelburne, N.S. The salmon were then shipped to New Brunswick for processing to be sold at market.

'There's not necessarily any evidence that these fish ... actually have the ISA virus ... all you need is a few fish, two or three ... [and] the whole facility [is] quarantined.'—Pamela Parker, Atlantic Canada Fish Farmers Association

ISA infection is fatal for 90 per cent of infected fish but poses no threat to human health directly or through consumption, according to the CFIA.

Paul Mayers, acting vice-president of programs for the CFIA, said processed salmon from ISA-infected fish meet all requirements for export to the U.S. because there is no risk to humans or wild salmon.

He said the exposed fish are only processed at facilities with a special ISA-processing licence.

"It is not expected that, that processing will have any impact on exports to the U.S. … the world organization for animal health provides explicit guidance: Two countries with respect to the trade in fish — regardless of ISA status — makes clear the fish fillets or steaks packaged for the retail trade are acceptable and can be traded safely," Mayers said.

"Like Canada, the U.S. takes a scientific approach to its decision-making. It respects international guidance and we would expect the same in this case."

Mayers stressed that the exposed fish that were sent to market were frequently monitored during the six months they were grown in the open-sea cages before being sent to the N.B. processor.

"Throughout the period that these fish were growing, CFIA continued to monitor and that included direct testing of fish for ISA in the other pens at the facility. By no means was our surveillance activities at the facility limited to just visual inspection," he said.

Mayers went on to say that should a fish show "outward clinical signs of the disease," they would not be considered acceptable for human consumption either in Canada or the U.S.

An ISA-infected Atlantic salmon displaying hemorrhaging on its skin and fin. (Univeristy of Maine)

On its website, the CFIA states that ISA symptoms include a loss of appetite, abnormal swimming patterns, gulping at the surface, grey gills, swollen abdomen, and areas of bleeding along the sides of the fish, and internally.

"ISA does not represent a risk to human health — that said, fish inspection regulations address the issue of the entry into the food supply of animals which are demonstrating clinical disease. Such animals on inspection would be rejected from entry into the food supply," Mayers said.

In an email to CBC News Friday afternoon, Theresa Eisenman with the U.S. Food and Drug Administration, stated, "Salmon with the ISA virus should not be entered into interstate commerce in the United States."

Eisenman clarified that salmon with ISA would also not be allowed across the border from Canada as it would be considered a violation of the U.S. Federal Food, Drug, and Cosmetic Act.

However, Eisenman did not make it clear whether that ban includes fish exposed to the virus that showed no outward signs of the disease.

A few infected fish can shut a facility

Fish from the Cooke Aquaculture facility in Shelburne were not confirmed to have ISA but were exposed to fish that tested positive for the disease.

Pamela Parker, the executive director of the Atlantic Canada Fish Farmers Association, said Friday it only takes a few fish to shut down an entire operation.

"There's not necessarily any evidence that these fish ... actually have the ISA virus ... all you need is a few fish, two or three ... [and] the whole facility [is] quarantined.

"So these fish ... even though they may have been around the virus, were not diseased and were perfectly safe for human consumption," Parker said.

Groups such as the Atlantic Salmon Federation have called on federal authorities to shut down open-sea salmon farming in favour of land-based tanks.

Parker said both the CFIA and the fish farmers association take ISA very seriously and said that open-sea farms are still the best option, taking into account risk of exposure to wild populations and overall cost of farming operations.

With files from the CBC's Jack Julian