“Yellow fish” issue in farmed Chinook salmon not linked to PRV, new study shows

Three heavy hitters in BC’s fisheries and aquaculture science community have published a new study after a laboratory challenge of several different species of salmon.

The study investigated the phenomenon of yellow (jaundiced) fish from a Chinook farming operation in Clayoquot Sound; the level of Piscene Reovirus (PRV) in these fish compared to other species; and any disease associated with jaundiced fish and PRV infection.

 

Activists have made much of finding yellow salmon but research shows there’s no connection with PRV or a disease only observed in Europe.

In our controlled laboratory exposure study, we demonstrated that PRV persisted in each of the Chinook Salmon, Sockeye Salmon and Atlantic Salmon for 5 months after ip challenge without resulting in microscopic evidence of HSMI or any other disease.

Our study supports the hypothesis that exposure to PRV is not solely responsible for the development of Jaundice Syndrome. It may be possible that the presence of PRV is not contributory towards jaundice in Chinook but rather that its association is merely a reflection of the ubiquitous presence of PRV in wild and farmed salmon species of BC.

The research supports the conclusion that in Pacific waters, PRV is not connected to the Heart and Skeletal Muscular Inflammation (HSMI) disease, and that there is no connection between PRV and the jaundice phenomenon in farmed Chinook salmon.

 

Salmon aquaculture virus study leaves one big unanswered question

A study by Norwegian researchers published late last month is apparently ” the first study confirming the presence of virus-infected escaped farmed Atlantic salmon in a nearby river shortly after escaping.”

The study makes some interesting speculations:

The recapture of the infected escaped salmon in nearby marine sites highlights the potential contribution of escapees in virus transmission to other salmon farms in the area.

…little is known about the effect of viral disease outbreaks in aquaculture on the wild salmonid populations. Disease outbreaks in salmon farms may lead to a substantial increase in infection pressure on wild fish in the surrounding area.

…escaped salmon may disperse over long distances, may enter rivers and may interact with wild conspecifics in their habitats. Therefore, an infected escapee may spread pathogens from the sea to wild fish populations in both sea and rivers distant from a disease outbreak.

That’s interesting, but there’s one big problem, which the researchers acknowledge.

…baseline data from the river regarding these viral infections in salmonids are lacking.

They cannot answer the question: how do the levels of viral loading on farmed salmon escapees compare to the natural viral loads in wild salmon?

As Yoda once said:

Too bad this flaw doesn’t stop their speculation.

This could have been an excellent study if the researchers had taken some time to get data on wild fish in the rivers where escapees were found and sampled. Of course, wild fish sampled from these rivers post-escape would not provide any valuable baseline data, but they could at least provide information about viral loading in wild fish.

And the researchers could have also gotten some control data from other similar rivers where no escapees are found.

But it seems that in the rush to be able to declare this paper the “first” at something, or because it was outside the scope of the finding grant, they decided to sacrifice context in favour of speculation.

At least it does provide some good information about viral loading in escaped farmed salmon in Norway. It will undoubtedly be valuable to the researchers that decide to investigate natural viral loading in wild fish in Norwegian rivers.