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:

ControlToo 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.

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