Sea lice


Salmon and trout farming entails a relatively higher level of host density compared to in the wild. Infection pressure of wild salmon stocks with sea lice from farmed salmon is one of the main challenges in terms of environmentally sustainable aquaculture.

Due to the host density in farming, Lerøy attempts to keep average numbers of mature female sea lice as low as possible throughout production. Combatting sea lice entails higher costs and have the highest priority in Lerøy.


Our ambitions in this area

Our ambition is to avoid lice by means of a successful IPM (Integrated Pest Management) system. The key parts of an IPM strategy are prevention, monitoring and control. As such, several measures complement each other and overlap in the efforts to keep salmon lice at a low level.

How we work in the area

We take targeted measures to reduce the number of lice by reducing exposure in the sea. To do so, we produce larger smolt using RAS technology so we can have shorter production periods in the sea. Biological delousing using our own produced cleaner fish is also a major target area for Lerøy.

Since 2010, Lerøy Seafood Group ASA (LSG) has developed technology for semi-closed facilities. This technology takes water from depths of 20-30 metres and transports this via a laminar flow in a tube. Water from these depths helps reduce infection exposure for the fish in the facility as the majority of lice larvae are found in the upper water layers, down to depths of 10 metres.

Requirements from the authorities provide a definition, at any given time, of the upper maximum limits for fully grown female lice. Lerøy has also established their own limit values to provide guidelines for when to implement preventive and active measures to combat salmon lice.

The average values for lice in the facilities shall be reduced by more than 50% during the period from April to June when compared with the rest of the year. This is when wild salmon migrate as smolt from the rivers to the sea.

How we measure our impact

Counts and registration are carried out minimum every seven days for all cages in each facility, by catching the fish in a landing net or other net. The fish are anaesthetised in tanks and studied individually.  A representative selection of fish is taken from each cage. Lice shall be counted in the following categories in terms of stages:

1) Adult female (with and without egg strings).

2) Moving (large and small).

3) Attached.

An average figure is calculated by totalling the number of all lice from all fish (plus lice in the tank for counting) and dividing this number by the total number of fish studied. The average for the farm is calculated by adding up all the average values for each cage and dividing this number by the total number of cages studied.

Infestation of wild fish by lice from Norwegian fish farms is calculated regionally by the Institute of Marine Research, by counting lice on wild salmon and using modelling. To read the Institute's report for 2021, use the following link:

Targets per KPI and Results per KPI

Target 2021: Average level of adult female lice not to exceed 0.11 lice per fish


2019: 0,15

2020: 0.16

2021: 0.18


Target 2022: No exceedances of limits set by the authorities 

Limits for levels of adult female lice per fish set by the authorities varies throughout the year and differ depending on region. This is described in detail in the Group´s Policy for control of sea lice.

Action taken due to results per KPI

Lerøy’s efforts to control salmon sea lice shall continue to follow the principles of an IPM strategy to control salmon sea lice and keep the numbers at a low level in the long term. The goal is to reduce the negative impact on the environment and the need for active interventions. Below is a description of the overall principles underlying this control strategy.

Preventive measures: Prevention is the first line of defence, aiming to control the levels of salmon sea lice by making use of passive control mechanisms. The methods utilised depend on local prerequisites, and entail use of one or more of the following measures: Structural measures relating to use of locality, zone collaboration, fallow periods in between production cycles, smolt quality and physical barriers.

Biological control: Cleaner fish represent a method for treatment prevention, and the goal is to reduce the need for active measures.

Non-medicinal methods: These methods are based on different types of measures that do not include the use of medicines. Lerøy makes use of methods within the categories for fresh water, flushing and temperate water.

Medicinal methods: These methods are based on the use of medicines. In cases where medicines are utilised, these shall be 1) prescribed by authorised fish health personnel and 2) evaluated with a view to the risk for fish welfare, food safety, environment and resistance, and 3) where only medicines approved by Norwegian medicines authorities can be used.