Sealice control


Dealing with lice is high on our stakeholders´ agenda due to the potential negative impact on wild populations and farmed salmon’s health and welfare alike. Treating lice is also cost and resource intensive, and high levels imply lower productivity and quality. Improper handling of lice can lead to resistant lice, which again could lead to natural constraints on future growth of the industry. In short: SeaLice management is decisive to secure long-term sustainability of the industry.


Lice levels shall stay below Norwegian authorities´ limit of 0.5 mature female lice in all our fish farms in Norway. We also strive to achieve the same levels in our operations in other countries. To ensure compliance we strive always to be ahead of lice outbreaks through continuous monitoring and response. Delousing efforts should also be balanced against fish welfare, avoiding resistance, and with regard to impact on the local community. We therefore favor non-chemical delousing methods when possible. For the best possible joint response, we will also focus on local cooperation, coordination and transparency towards other participants.


A key step in our efforts to prevent and treat against lice is the statutory systematic monitoring of sea lice levels in all our fish farms. The salmon are checked for lice every week at water temperatures above 4°C. At water temperatures below 4°C lice are counted every other week, out of consideration for fish health and welfare. In BC, we follow local regulations adapted to the local sealice situation. Counting is performed with different intervals, and requiring motile stages in the development of the lice. Based on the results, relevant measures are applied. Examples of such measures include conducting lice counts several times a week at high sealice levels, as well as susceptibility testing of sealice populations before treatment engages.

All regions shall have a comprehensive plan for sealice control. In 2016, we have held meetings in our interregional production manager group, where sealice is a recurrent issue, to discuss best practices for managing and monitoring lice levels, including the regional plans.

Revolving use of the fewest possible chemical agents is extremely important in lice treatment, in order to minimize the development of resistance to available treatment, and limit the impact on the local environment. We have therefore focused on “rolling over” the use of chemical agents and active use of wrasse. In Rogaland, we now have extensive and positive experience with the use of wrasse. Unfortunately, natural conditions are not right for the traditional use of wrasse in the other regions, implying the use of alternative methods. The last four to five years, we have commenced projects attempting to develop the use of lumpsuckers in Rogaland, Finnmark and Shetland.

We register an unfortunate tendency among sealice towards lower susceptibility to medical treatments. In 2016, this led to a thorough assessment of several, alternative, non-chemical treatments options. This has implied an increased use of lice skirts designed to protect newly released smolts in the sea in Finnmark and Shetland. In addition, delousing by means of heated water, so-called thermal delousing, has been carried out in Norway and UK.

In course of 2016, intensified efforts were made in BC, in order to obtain approval for treatment with hydrogen peroxide. We also cooperate with other actors in the regions where we operate to keep sealice levels low.

Chart 4 shows the average monthly level of mature female lice in each region of Grieg Seafood. Sealice remains a huge challenge. In Finnmark and Rogaland, we manage to keep sealice levels down, yet only at a high price. Scotland records a situation with higher sealice levels than the other regions. Sealice numbers have somewhat decreased from 2015 to 2016, although with significant local variation.

The trend in BC causes some concern, as sealice levels have increased throughout the year, and in one specific area, the lice show reduces susceptibility towards emamektin.

In Rogaland, the combination of wrasse and 100% clean nets has been an important factor in keeping sealice levels low. Good grooming of wrasse is also important, and good hiding places and feeding of wrasse in periods with little lice is important.

Charts 5 and 6 show the amount of medical active substances used for in-bath and in-feed treatments respectively, in order to remove sealice from the fish. Shetland had a 50% reduction in the use of in-bath treatment, but registered a somewhat higher consumption of in-feed emamektin. In Rogaland, the in-bath treatment is quite stable, while delousing agents in feed is slightly growing. In-feed treatment is used for smaller fish. In Finnmark, the consumption of in-bath substances is sharply reduced (except for H2O2 which is exempt from the statistics), while some emamektin is still used in-feed. The main reason for this is increased use of peroxide (H2O2) as well as mechanical treatment. BC has little use of the treatment, which is due to a deliberate limitation of the number of treatments per year to reduce the risk of sealice becoming resistant to the most commonly used active substances. It is important to notice that sealice levels are managed and kept low during the sensitive wild salmon out migration three month period.


We have defined a target of not more than an average of 0.5 sexually mature female lice per site. Although this is more stringent than the requirement for localities outside of Norway, we wish to strive towards the same goal throughout the Group, also in BC and Shetland. For green licenses in Finnmark, the goal is as low as 0.25 sexually mature female lice. In addition, we have an overall goal of 50% reduction in treatments over the period 2015-2018.

To ensure that we achieve our goal of combating lice while avoiding resistance, we will continue to make necessary investments to implement the most effective treatment methods. In this work, we keep a focus on non-chemical treatments. We have acquired significant extra capacity for so-called thermal treatment (heated water) by keeping available Thermolicers in the three most afflicted regions: Finnmark, Shetland and Rogaland. In addition, we will expand the use of sealice skirts in Finnmark and Shetland. We will also continue our efforts to make the lumpfish a more effective lice-eater. Recently, we decided to install lice lazers at a site in Rogaland, in order to perfom a full-scale test of this technology.

GSF is also part of a cluster in Bergen, NCE, which is host to a “Big data” pilot project deploying large amounts of data and processing power into the search for new approaches to fight sealice more effectively.

* The general legal limit for sea lice in Norway. We have implemented this limit internally in the UK and Canada, even though the legal maximum is higher in these countries.