Facts about salmon lice
Salmon lice (Lepeophtheirus salmonis) occur naturally in all marine areas of the Northern Hemisphere. It is the most common parasite found on wild and farmed salmon and can cause wounds on the fish, which may lead to infections.
Salmon lice are small crustaceans that develop through eight life stages. In the early stages, they drift with water currents and can spread over relatively large areas. It does not affect the food safety or quality of salmon but poses a major challenge for the aquaculture industry.
Once a salmon louse attaches to a fish, it continues to grow and eventually develops into an adult louse that can reproduce. To protect wild and farmed salmon, limits have been set on how many salmon lice are allowed on fish in aquaculture facilities.
Fish farmers must regularly count and report salmon lice levels, treatments and seawater temperature to the Norwegian Food Safety Authority. Reporting is required weekly when the seawater temperature is 4°C or higher, and every two weeks when it is below 4°C.
What are salmon lice?
- Salmon lice (Lepeophtheirus salmonis) are natural inhabitants in seawater in the Northern Hemisphere
- Salmon lice feed on different parts of the fish, which can cause wounds and damage to the fish
- Salmon lice infestation is dependent on temperature, and warmer seawater can lead to more lice
- The extent of salmon lice infestations is also dependent on the quantity of fish in an area
- Since 2013, a national surveillance program for salmon lice has been tracking the development in Norway
What is being done to improve the fish mortality level?
Fish welfare has come under intense scrutiny in the Norwegian aquaculture industry. In 2023, the sector faced a particularly difficult year, with serious challenges linked to pearl jellyfish and winter ulcers disease.
However, figures from the Norwegian Veterinary Institute now show that mortality in the aquaculture industry declined in 2024 and 2025 compared with 2023 (report in Norwegian). The number of disease cases and the share of fish lost during production are also decreasing in several areas.
As good fish welfare is part of responsible and economic viable fish farming, any salmon farmer would benefit from reduced mortality. A holistic approach to biosecurity is necessary to reduce the risk of disease and ensure a healthy upbringing of the fish.
Biosecurity initiative in the aquaculture industry
2024 marked a milestone as the industry’s large-scale biosecurity initiative was launched (Norwegian website). The goal has been to establish a shared understanding of how to develop national best practice to prevent infection between sites and thereby reduce the risk of disease outbreaks.
Biosecurity in aquaculture involves strict hygiene routines, zoning, vaccination programmes and continuous monitoring of fish health.
The industry has already made great progress, and initiatives such as Seafood Norway's biosecurity work have contributed to more effective measures and better interaction in the industry.
Hundreds of millions of Euros are being invested in research and development of technology every year to improve the different aspects of the situation.
Examples of biosecurity measures in Norwegian aquaculture:
- Postponed release of the smolt: Instead of being moved to the pens in the open sea when they are small and fragile (500 gram), the smolt are now 1-2 kilograms. The large smolt are stronger and more robust to sea lice.
- Use of lasers: Thanks to modern technology and artificial intelligence, the laser signals can find and destroy the sea lice – without harming the salmon.
- Many salmon companies are lowering the fish pens deeper into the sea to a level where the parasites cannot survive. This way, salmon is protected from sea lice.
- Development of new and better vaccines.
- The use of partially enclosed pens also provides additional protection for the fish.