Nodavirus Detected In Norweigan Farmed Cod

Will fight new cod disease - NORWAY - Nodavirus has been detected for the first time in cod in Norway. New research results at Fiskeriforskning can prove to be important in the fight against the virus.

Earlier this week, the National Veterinary Institute and the Norwegian Food Safety Authority reported that the nodavirus, which has previously affected both halibut and turbot fry in Norway, has been detected for the first time in Norwegian farmed cod.

The virus can cause the disease viral nervous necrosis (VNN) in the fish that becomes infected. The result can be reduced appetite and high mortality.

Fry most vulnerable

Together with Engineer Saskia Mennen and others, Senior Scientist Ann-Inger Sommer has spent several years studying infection by nodavirus in halibut, spotted wolffish and cod. Sommer says that in the cod, as in the other fish species, the fry are most vulnerable to the disease after infection through the water.

Tests have shown that the smallest cod fry became sick after infection with a nodavirus from Norwegian farmed cod. During the two-month test period, 56 % of the cod fry died that weighed 0.5 g when infected via the water.

Conversely, the larger fry that weighed 5 g did not die of infection via the water. In this group, 35 % died of VNN when they were infected through injection of the virus into the fish.

High temperature causes higher mortality

The last tests also show that when the temperature in the water rises, there is a pronounced increase in mortality in the fish that are infected with the virus.

Fry weighing 5 g that were infected by injection of the virus suffered 60 % mortality in water that was kept at around 15 degrees Celsius. In cooler water, the mortality rate was much lower.

"The tests show that the infected cod is far more likely to die of the nodavirus if the water temperature rises", says Sommer.

So, what can be done to prevent this virus from becoming a big problem for cod farming?

Using challenge models in the fight against the disease

The research results at Fiskeriforskning are the beginning of a challenge model for the disease VNN in cod, on a level with the model scientists at the Institute have created for the viral disease IPN in salmon.

For example, such a challenge model can help the scientists create a vaccine against VNN in cod. It can also be used in the cod breeding programme to select the cod families that are hereditarily most resistant to the disease.

"When complete, the model will also help us learn how the cod thrives best in farming conditions. A fish that that thrives also has a better immune defence", says Sommer in closing.

The research is financed by the Research Council of Norway, Innovation Norway and Fiskeriforskning.

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