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Search for salmon disease goes high tech

The Daily Gleaner


Search for salmon disease goes high tech


NEVILLE CRABBE COMMENTARY



Aquaculture cages in Bliss Harbour, at the exit of Passamaquoddy Bay, showing the tight spacing. Photo Tom Moffatt/ASF


Fish health has long been a preoccupation in hatcheries and aquaculture operations.


When millions of fish are crowded into tanks and sea-cages, diseases like infectious salmon anemia and pancreatic necrosis spread fast with deadly consequences.


Profits and reputation often suffer alongside the animals.


Until now, the same intense focus on fish health has not been applied to wild populations.


Thatís changing with the advent of a powerful new technology and recognition that viruses from aquaculture sites drift into the environment, something the Cohen Commission in British Columbia made clear.


Officially known as the Commission of Inquiry into the Decline of Sockeye Salmon in the Fraser River, Justice Bruce Cohen heard from 179 witnesses and reviewed nearly 900 public submissions before issuing a three-volume final report in 2012.


Fraser River sockeye migrate past open net-pen salmon cages on their way to ocean feeding grounds and Cohen concluded that, ďI accept the undisputed evidence that there is some risk posed to wild Fraser River sockeye salmon from diseases on salmon farms, Ēbut a lack of data meant he was unable to say how great the risk is.


The uncertainty led Cohen to recommend that Fisheries and Oceans Canada begin studying which pathogens Fraser River sockeye encounter during their migration, and the likelihood of catching disease from aquaculture sites/ A few months after Cohenís report was released, DFO created the Strategic Salmon Health Initiative and put high profile geneticist Dr. Kristi Miller in charge.


Partly funded and staffed by NGOs like the Pacific Salmon Foundation, the team has developed a powerful virus hunting tool that can detect 45 different pathogens in organs and flesh even before disease occurs.


In 2013 the Strategic Salmon Health Initiative gathered about 30,000 samples from wild, hatchery, and aquaculture salmon.


In 2016, testing began and already it has produced explosive results.


Samples from one aquaculture site tested positive for Heart and Skeletal Muscle Inflammation(HSMI), the first definitive diagnosis of this deadly fish disease in Canada.


Originally detected at Norwegian aquaculture sites in 1999, HSMI has also spread to Scotland and Chile.


It causes heart lesions and can kill 20 per cent of infected fish, but itís extremely contagious with up to 100 per cent of fish testing positive at aquaculture sites where there is an outbreak.


Salmon with HSMI begin swimming strangely and often stop eating.


Aquaculture fish may recover, shielded from predators and fed a constant diet of pellets, but these symptoms would put wild fish at risk in the harsh ocean environment.


The Strategic Salmon Health Initiative is set to wrap up its work and publish results by 2020, but some researchers are already making direct links between industry disease and declining wild Pacific salmon populations.


In December 2017, Alexandra Morton and two scientists from the Atlantic Veterinary College published peer-reviewed scientific evidence that large numbers of wild salmon were being infected by viruses spilling out from B.C. salmon farms with dire consequences.


Like HIV causes AIDS, HSMI is almost certainly caused by the piscine orthoreovirus, known as PRV.


There are arguments that this is inconclusive, but every single diagnosed case of HSMI has tested positive for PRV, and no one has been able to reproduce HSMI in a laboratory without PRV.


Tests by the B.C. Ministry of Agriculture have confirmed the PRV virus is present in 80per cent of farmed salmon in the province.


Itís not surprising then that Morton and her team found levels of PRV infection in wild fish depended on how close they were to the aquaculture industry.


Up to 45 per cent of B.C. wild salmon that were highly exposed to salmon aquaculture tested positive for PRV compared to 5per cent of salmon further away from the industry.


In the Fraser, the researchers found that PRV infection rates were 50 per cent higher in fish sampled from lower sections of the river compared to salmon tested in the upper stretches, beyond challenging obstacles like the Hellís Gate rapids.


They concluded sick fish were less able to reach their spawning grounds, something that could have a population level effect on the Fraser River sockeye.

 

On the East Coast, wild Atlantic salmon are suffering a similar fate with nearly twice as many dying at sea compared to the 1970s and 1980s.


The result is fewer fish making it back to their home rivers to spawn.

 

Like the Pacific situation, not much is known about the role of disease and transmission from aquaculture sites.


What we do know is that wherever there are open net-pen salmon farms in Atlantic Canada wild salmon populations have crashed, like the Bay of Fundy and the south coast of Newfoundland.


So, earlier this month ASF researchers shipped samples collected close to and far from East Coast aquaculture sites to Kristi Millerís lab for analysis.


These include tissue from wild Atlantic salmon and recent aquaculture escapes.


The results will tell not only if acute, lethal diseases are present in wild Atlantic salmon, but also what viruses might be weakening fish and making them prone to predators or other infections.

 

NEVILLE CRABBE is director of communications for the Atlantic Salmon Federation.