Concern as BKD spreads in central Norway

Bacterial kidney disease (BKD) has been detected at several locations in central Norway since the start of the year, the country’s Veterinary Institute has reported, and its spread is slightly puzzling marine veterinarians.

Salmon farms are mainly being affected but there has been at least one incident involving a trout farm.

The development is the latest in various biological issues affecting parts of the Norwegian coast this year.

• Infectious salmon anaemia (ISA) has also been prevalent, with the number of outbreaks in the first half of this year already passing the total for 2022.
• The main areas affected by BKD include Trondelag, More and Romsdal counties and the Vestland region.

The Institute says BKD is caused by infection with the bacterium Renibacterium salmoniarum. The bacterium grows slowly, and it can take a long time to show clinical signs after fish become infected.

BKD is a chronic disease and was first reported in the wild Atlantic salmon populations in the rivers Spey and Dee in Scotland in the early 1930s.

Subsequently BKD has been found in both wild and farmed salmonid populations in Norway, North and South America, continental Europe and Japan.

Clinical signs include darkening of the skin, pale gills, fluid in the abdomen distended abdomen, protruding eyes and pinpoint bruising. Fish appear anaemic and lack food in the gut. The liver, kidney and spleen are often pale.

The Institute said the primary source for the latest infections is unknown, but it thought that wellboats, delousing vessels and other fish farming equipment have contributed to the spread of the disease along the coast of central Norway.

It is now in the process of whole-genome sequencing of bacteria that have been cultivated in connection with this year’s outbreak and previous outbreaks, and the results should reveal whether it has resulted from a single introduction or several.