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Until now, a pathologist seeking to determine a salmon’s cause of death might scrutinize a set of tissue samples under a microscope or culture a bacterial or viral sample over several days to isolate the cause of the disease.
All of that is changing fast at the federal Pacific Biological Station (PBS) in Nanaimo, British Columbia, where researchers have created a novel, game-changing shortcut that sleuths out systemic infectious diseases—even before the fish is obviously sick. “It’s really going to be powerful,” says Kristi Miller, who heads the salmon genetics section at PBS.
Using little more than a tiny tissue sample from a salmon’s gill, researchers can identify the presence of unique biological markers that reveal not only if a fish is suffering from an infectious disease, but whether it harbors a disease agent that is not yet obvious.
“Just because you detect an agent, doesn’t mean it has a disease,” says Miller. “We all walk around with little bits of flu bugs and things all the time.”
Miller’s lab has compiled a database of 51 disease agents and can check tissue samples against 47 of them at a time. Some agents are associated with emerging diseases that have not yet been detected on Canada’s Pacific coast, but have been seen elsewhere, whether in aquaculture settings or in the wild. The test is a rapid, broad analysis of a fish’s possibility of getting sick or of passing the disease on to others. Currently, only viral diseases can be detected at the early stage, but Miller’s lab is also working on developing similar tests for bacterial and parasitic diseases.
Miller and her colleagues already employ molecular genetics technology to help identify small, vulnerable salmon stocks that are at risk of being caught while traveling with much larger, healthier runs. The same technology is also being used to identify salmon and track their migrations.
Now, Miller’s work should also provide a way to track the emergence of novel diseases and better understand the transfer of disease between farmed and wild fish.
“You cannot look at infectious disease without questioning the risk of aquaculture,” she says. British Columbia “is the only part of the world where we have a burgeoning aquaculture industry and really big abundances—still, even though they’re in decline—of salmon stocks that are very important commercially.”
Miller says there is “obviously a theoretical risk” of farmed salmon transferring disease to wild stocks, and through her research she is seeking to isolate the diseases of greatest concern. “If we can determine that, we could vaccinate the aquaculture fish and there might be a solution to minimize the risk.”
Miller’s lab has so far processed 16,000 fish with another 10,000 to go to create a rigorous databank identifying diseases present in BC fish and those that pose the greatest threat. This information is “going to lead us down places we wouldn’t have been able to go,” she says. “This is the most powerful thing I have in my hands.”