Laboratory tests showed that the bacteria Pasteurella atlanticus became inactive within approximately one hour when exposed to 100% freshwater.
The Pasteurella bacteria, which causes pasteurellosis in Norwegian farmed salmon, does not appear to survive long in freshwater, according to research conducted by the Norwegian Veterinary Institute as part of the Pasteurellosis in Norwegian Salmon project.
This finding follows an epidemiological study indicating that the likelihood of pasteurellosis outbreaks significantly increases after thermal or physical delousing in seawater but not after freshwater-based treatments.
“Previous work has shown that fish carrying the bacteria may release it during stressful handling. This raises the question of whether freshwater delousing could reduce both the severity and frequency of outbreaks,” said senior researcher and project leader Duncan Colquhoun.
The project is funded by FHF and aims to better describe the bacteria and understand why it has become a significant issue in Norwegian aquaculture. Further findings will be presented at the Havbruk 2024 conference in Tromsø from October 22-24.
Pasteurella in farmed salmon, specifically the bacterium Pasteurella atlanticus, causes a disease known as pasteurellosis. This bacterial infection can lead to significant health issues in salmon, including:
- Eye Infections: One of the common symptoms is severe inflammation of the eyes (conjunctivitis), which can lead to red, swollen eyes and, in advanced cases, blindness.
- Skin Lesions and Ulcers: Infected fish may develop sores or ulcers on their skin, which can become sites for secondary infections.
- Internal Infections: The bacteria can spread internally, affecting organs such as the liver, spleen, and kidneys, causing systemic infections.
- Lethargy and Loss of Appetite: Infected salmon often become lethargic and stop feeding, leading to poor growth and increased mortality rates.
- Mortality: In severe cases, pasteurellosis can lead to high levels of mortality, especially when outbreaks occur in farming conditions where fish are stressed due to handling or environmental factors like delousing treatments.
