Fresh water ‘may be answer to salmon disease’

The bacterium that causes pasteurellosis in farmed salmon does not survive for long in fresh water, new tests have shown.

Experimental work has been carried out by the Norwegian Veterinary Institute in this area which has thrown up some interesting results.

The Institute says that the pathogenic bacterium Pasteurella has become more widespread in Norwegian fish farming in recent years and is also developing into a major problem for the industry.

Pasteurellosis has become an extremely serious disease, particularly in south-western Norway, and is now the third most import bacteriological issue for salmon farming, says the Institute.

Now, a three-year project led by the Norwegian Veterinary Institute and financed by the Norwegian Food and Agriculture Organization (FHF) is providing more knowledge about the bacterium and how to combat it.

The report states: “Experiments with fresh water were carried out after an epidemiological investigation showed that the probability of an outbreak of pasteurellosis increases significantly after thermal or physical de-lousing with seawater, but not after freshwater-based de-lousing.

“In the laboratory experiment, it was investigated how long the bacterium Pasteurella atlanticus survives in water with different salt concentrations. But when exposed to 100% fresh water, the bacterium was inactivated within approximately one hour. “

Senior researcher and project manager Duncan Colquhoun said: “Previous work has also shown that hidden infected fish secrete disease-causing bacteria during stressful handling.

“There is, therefore, reason to look more closely at whether freshwater-based lice removal can reduce the severity and number of disease outbreaks after such treatments.”

More results from the project will be presented during the two-day conference Havbruk 2024 in Tromsø which starts on Tuesday.