Mapping salmon welfare: sea lice treatments

For any queries, please contact hannah@rethinkpriorities.org

Executive summary

This report provides a factual overview of the landscape of sea lice treatments in the salmon farming industry and how they affect animal welfare.

• Sea lice directly harm salmon, both farmed and wild
• Sea lice are a ubiquitous problem in salmon farming
• Governments regulate permitted sea lice levels
• Producers try to prevent sea lice, but methods are not 100% successful
  • Millions of cleaner fish (small fish species that eat lice from salmon) are used annually to try to prevent lice infestations, but many suffer severe welfare harms
• Pharmaceutical treatments can be used to treat lice, and are relied on in Chilean salmon farming
• Due to concerns of lice resistance and harms to wildlife, Norwegian producers began using physical treatments (methods that physically remove lice from fish)
  • Popular physical methods are thermal delousing and mechanical delousing—both methods involve intensive handling of fish and crowding in treatment chambers
  • Thermal delousing: salmon are submerged in hot water to detach lice, causing salmon to show panic escape behaviors, head shaking, and collisions, indicating pain and distress
  • Mechanical delousing: salmon are pumped through high-pressure water jets or brushes to dislodge lice, often damaging gills, eyes, fins, and skin, sometimes leading to brain hemorrhage and death
• Some certification schemes provide standards for improving welfare when physical methods are used, but many give no specific guidance on key parameters like temperature and duration
• Welfare-minded innovation is needed to develop new, scalable sea lice treatments that do not cause animal welfare harms

A visual depiction of the high-level reasons for sea lice treatment choice is below:

Incentives for sea lice treatments

Background: What are sea lice?

Sea lice are parasites that attach to salmon skin and feed on their blood and mucus. While naturally occurring in wild populations, the high density of farmed salmon in close proximity creates ideal conditions for rapid lice reproduction and spread. Sea lice can cause multiple welfare harms to salmon: direct injury, increasing infection risk via open wounds, and reduced growth. Several industry experts identify sea lice infestations and their treatments as top welfare issues for farmed salmon.^[1]

All major salmon farming countries are affected by sea lice. Some estimates suggest approximately 9% of farm revenue can be lost to sea lice^[2]. Annually, sea lice could cost the Norwegian salmon farming industry approximately NOK 6.6 billion.^[3]

In this short report, we discuss four broad categories of sea lice treatments. These are described in Table 1. We consider each in more detail below.

Table 1: Categories of sea lice treatments, with examples and the main problems with their use.
Table 1: Categories of sea lice treatments, with examples and the main problems with their use.

Figure 1 provides an overview of the main reasons and patterns causing producers to use different delousing treatments. We describe these in more detail below

Figure 1: Flow diagram showing the main overarching reasons for shifts in sea lice treatment patterns.

Governments regulate sea lice abundance

Governments regulate the number of sea lice that are allowed in marine net pens to:

• Protect wild salmon populations from the transmission of sea lice that spread from farms to wild fish during their migration
• Improve farmed salmon welfare by preventing lice infestations from reaching levels that cause severe injury, stress, reduced growth, and mortality in farmed fish
• Mitigate economic costs to producers by preventing infestations from reaching levels that would require emergency treatments, cause mass mortalities, or instigate cascading outbreaks to multiple farms

Regulations limit permitted sea lice levels

Sea lice follow predictable seasonal patterns, with warmer water accelerating their reproduction and development—a pattern visible across all salmon farming regions (Figure 2). Governments have responded by setting strict limits on acceptable lice levels, but these vary by country and context. The national sea lice limits in the main producing countries are as follows (also see Figure 2):

• Norway: <0.5 adult female lice per fish, <0.2 during wild salmon migration
• Scotland: Reporting required at 2 adult females per fish, intervention required at 6 adult females per fish
• Faroe Islands: 1 adult female per fish
• Chile: 3 gravid (carrying eggs) adults per fish
• Canada: 3 motile (able to move) sea lice per fish during wild salmon migration period (March–June)

These regulatory frameworks, combined with the economic need to prevent lice-related losses, create pressure for intervention.

Figure 2: Monthly sea lice count per fish in major salmon-producing countries from 2013–2024. Dashed yellow lines show governmental sea lice limits (seasonal limits not included). Source: Global Salmon Initiative (GSI) 2024 Sustainability Report. Because not all companies are part of GSI, the data likely does not represent true country-level ranges. The number of companies present in the data in 2024 is given next to the country name.

Preventative methods sometimes fail, leaving producers dependent on reactive treatments

Sea lice skirts and snorkel nets exploit sea lice behavior to prevent them from attaching to salmon (Figure 3). Sea lice are phototactic (attracted to light) and concentrate in the top few meters of water. Sea lice skirts create a barrier around the upper six meters of pens—permeable to water but blocking lice passage. Snorkel nets keep salmon below the lice-infested surface zone while providing a narrow tube to access the sea surface for swim bladder inflation, an essential behavior that allows fish to remain buoyant and control their depth.

Figure 3: Simplified diagram of a sea lice skirt and snorkel net

Both methods show good efficacy when properly implemented—skirts can reduce infections by around 80%^[5] and snorkel nets by 75%.^[6] They also have minimal welfare downsides, with reduced oxygen flow being the main potential concern.^[7] Sea lice skirts are commonly used in Norway, but there are no standard practices for when and how they are used.^[8] Snorkel nets have not yet been widely adopted by the industry.^[9]

However, preventative methods do not eliminate lice exposure entirely, so farmers must use available treatments to avoid exceeding thresholds and facing regulatory consequences (such as fines), even when these treatments harm welfare.

The welfare harms of sea lice treatments

While preventing sea lice from entering the net pen is preferred, when this fails, other treatments become necessary, and often carry welfare costs. Producers can deploy cleaner fish as an ongoing biological control measure, but when breakthrough infestations occur, they must turn to medicinal or physical treatments (see Table 1 above). The use of these methods has varied significantly over time and still differs geographically.

The rise of physical treatments and their harms in northern regions

While northern regions previously relied predominantly on medicinal lice treatments, by 2024, physical methods comprised the majority of sea lice treatments in Norway (Figure 4). This transition was driven by two key factors: environmental concerns and the widespread evolution of lice resistance to available medicines.

Figure 4: Treatment weeks (number of weeks in which a treatment took place) for medicinal and physical delousing treatments in Norway 2012–2024. Note that “Physical” includes thermal, mechanical, freshwater delousing, and combinations of these. Data from the Norwegian Directorate of Fisheries via the Norwegian Veterinary Institute (Moldal et al., 2025, Table 9.1.2).

The most commonly used physical delousing methods are thermal and mechanical delousing (Figure 5). In Norway, there were 1,072 “treatment weeks” of thermal delousing and 1,287 weeks of mechanical delousing in 2024. Mowi, the world’s largest salmon-producing company, estimated that 63% of its salmon experienced a non-medicinal sea lice treatment in 2024.

Figure 5: Treatment weeks (number of weeks in which a treatment took place) for different types of physical delousing treatments in Norway 2012–2024. Data from the Norwegian Directorate of Fisheries via the Norwegian Veterinary Institute. (Moldal et al., 2025, Table 9.1.2).

More recently, the industry has moved toward combining multiple physical approaches. Combination treatments^[10] rose from 3% of treatment weeks in 2020 to 18% in 2024, driven primarily by pairing thermal and freshwater methods,^[11] which increased fifteen-fold over this period. This rise suggests that single physical treatments are becoming insufficient for effective lice control.

Thermal and mechanical methods cause pain, stress, and increased mortality

Physical treatments operate through fundamentally different mechanisms than medicines—they work by creating conditions that physically harm or stress sea lice enough to kill them or cause them to detach. However, because sea lice and salmon have evolved in the same marine environment, they often share similar physiological vulnerabilities.^[12] This shared evolutionary history means that methods designed to harm sea lice frequently harm their salmon hosts as well.

In practice, this means the industry’s most relied-upon treatments could cause a lot of suffering. For thermal delousing, salmon are crowded and pumped from net pens into chambers of hot water for around 30 seconds.^[13] While this heat causes lice to detach, it also causes salmon panic and extreme pain, visible through escape-like behaviors, such as surface-breaking, head shaking, and collisions.^[14] The effects can persist for days after treatment, with salmon showing slower growth, reduced immunity, worsened gill health, and increased mortality.^[15] Secondary infections are also common.^[16]

Mechanical delousing presents similar welfare concerns. Fish are pumped through water jets to dislodge lice. In severe cases, this process can cause brain hemorrhage and death.^[17]

Both treatments require intensive fish handling—crowding in net pens, pumping through equipment, and confinement in treatment chambers, which risks damaging fish gills, eyes, fins, and skin.^[18] These stresses compound the direct treatment harms. Norwegian salmon producers have consistently ranked injuries from delousing treatments as the highest cause of poor welfare for seven consecutive years.^[19]

It is possible that freshwater baths cause less welfare harm than thermal or mechanical methods as it is often perceived by producers as gentler.^[20] Welfare concerns stem primarily from handling and crowding inherent to most physical methods,^[21] and from how long salmon can osmoregulate (maintain optimal water–solute balance) in freshwater. Some evidence suggests freshwater is more effective for controlling sea lice, though results vary,^[22] and lice may be capable of building resistance over time.^[23] Widespread adoption also faces logistical barriers around sourcing freshwater and water quality management during hours-long baths.

Adding more fish to the system: The welfare of cleaner fish

Millions of cleaner fish are used each year

Alongside the shift to physical treatments, the industry also adopted cleaner fish—small species like lumpfish and wrasse that eat lice directly from salmon. This biological approach gained widespread adoption as part of the broader move away from medicinal treatments. Populations reached 52 million in Norway by 2019, though recent years show a decline to 31 million by 2022. Scotland follows a similar pattern (Figure 6). That said, the Scottish branch of Mowi recently announced its intention to increase wrasse production to 1.2 million per year.

Figure 6: Number of cleaner fish in (A) Norway and (B) Scotland over time. Data from Norwegian Directorate of Fisheries (via Norwegian Veterinary Institute Fish Health Report 2025; 2024; 2022; 2021; 2020) and Scottish Fish Farm Production Survey 2023 (Table 42).

Cleaner fish suffer from starvation, stress, and 40% mortality rates

While cleaner fish may reduce some physical treatment harms to salmon, thermal and mechanical treatments are often still required to treat salmon. Cleaner fish themselves also experience severe welfare problems: mortality rates average 40%, with some farms experiencing complete die-offs.^[24] Deaths and poor welfare may result from starvation,^[25] exposure to the same harmful treatments meant for salmon,^[26] poor environmental conditions like a lack of shelters,^[27] diseases, and cataracts.^[28]

Whether cleaner fish effectively control lice remains contentious—studies show variable results.^[29] This limited efficacy could stem from cleaner fish being opportunistic feeders who may not frequently choose to eat lice.^[30] Therefore, on farms, they may not consume enough lice to meaningfully reduce populations.

Chile follows a different path—for now

While physical treatments now dominate in Norway and Scotland, Chilean farms have avoided these methods, instead continuing to rely primarily on pharmaceutical medicines for sea lice management. Chilean regulations allow for higher lice levels (3 gravid adults per fish compared to Norway’s 0.2–0.5) and maintain more permissive regulations around medicinal treatments, partly due to the absence of effective physical treatment infrastructure. However, this situation may not persist. Facing the same chemical resistance pressures, Chilean farms could soon adopt the thermal and mechanical methods now prevalent elsewhere, potentially affecting millions of additional fish.

Chilean regulations prohibit the use of non-native cleaner fish species. This restriction is designed to protect Chile’s native marine ecosystems from invasive species that could disrupt local biodiversity. However, researchers in Chile are actively working to identify native cleaner fish species that could provide biological control of sea lice, though progress has been limited, and we are not aware of any commercially viable cleaner fish program that has been established to date.

Future directions

The limited effectiveness of cleaner fish, combined with the welfare costs of physical treatments, leaves the industry in a difficult position. With regulatory pressure for lice control remaining constant, producers have few options, and each carries different welfare costs. However, several approaches could improve this situation.

Higher welfare protections when producers use harmful delousing methods

Since producers will likely continue using physical treatments in the near term, one incremental improvement would be establishing stronger welfare safeguards around these procedures. Currently, certification schemes establish sea lice monitoring requirements but show gaps in protecting fish from harmful treatments.^[31]

The Global Animal Partnership (GAP) standards allow mechanical delousing but do not permit use of thermal delousing. RSPCA Assured is the only major standard with temperature requirements, setting maximum temperatures at 34°C and limiting exposure time to 35 seconds. RSPCA Assured also limits pre-treatment starvation to 48 hours for mechanical delousing and 72 hours for thermal delousing. GlobalGAP requires any treatments to be prescribed by a veterinarian.

For cleaner fish, GAP standards include the use of hides and refuges, as well as daily supplemental feed. GAP also restricts cleaner fish annual cumulative mortality to 10%. Similarly, Best Aquaculture Practices (BAP) dictates “provision of shelter for them in the cages and supplemental feed” and that they should be separated from salmon before treatments. RSPCA Assured and GlobalGAP include requirements for a risk assessment or management plan to be in place.

Several gaps remain in certification schemes to protect the welfare of both salmon and cleaner fish. In particular, restricting use of cleaner fish, setting specific temperature and crowding limits, or prohibiting thermal delousing may help improve welfare during physical treatments.

Preventative methods seem promising but haven’t solved the problem yet

Though preventive methods like sea lice skirts and snorkel nets are somewhat successful, the continued high frequency of thermal and mechanical treatments suggests either that adoption of preventive technologies remains incomplete across the industry, or that even well-implemented prevention systems require backup treatments when breakthrough infections occur.

If prevention methods fail to control sea lice within regulatory limits, and available treatments work but cause severe welfare harms, the industry needs new solutions.

Welfare-minded innovation is needed

One promising approach is shifting toward relatively less harmful methods. Less harmful alternatives may exist, but face barriers.

Innovative technologies are emerging that could help the welfare problems caused by sea lice and treatments, though many are yet to be stringently tested for efficacy or welfare outcomes in commercially relevant settings. Blue Lice, a Norwegian company, developed blue light traps that capture sea lice larvae before they attach to fish. Stingray Marine Solutions developed underwater laser systems that use machine vision to identify and kill individual sea lice—multiple major producers, including Cermaq and Nordlaks, have deployed their laser systems, but commercial-setting trials have shown mixed results.^[32] Other innovations include electromagnetic fences, bubble curtains, and submersible cage systems that keep salmon away from surface-dwelling lice larvae.

Welfare-minded innovation is needed. While the industry is strongly incentivised to find new methods of controlling sea lice, it is not guaranteed that new methods will be good for salmon welfare. For example, closed systems like Recirculating Aquaculture Systems (RAS) could, in theory, prevent sea lice infestation by providing producers with much greater control over their water source, allowing them to source seawater from depths where sea lice eggs and larvae are not present.^[33] However, it remains unclear whether RAS would benefit salmon welfare overall,^[34] since the welfare benefits of eliminating sea lice exposure and greater control over water quality more broadly must be traded off against the welfare risks of the much higher stocking densities typically required to make these land-based systems commercially viable.

Moreover, current harmful treatments still have scope to expand. Chile may soon face the same chemical resistance pressures as other locations and, unable to use cleaner fish due to regulations against non-native species, Chilean farms could adopt thermal and mechanical methods.

The current treatment landscape affects hundreds of millions of farmed salmon annually, and has added tens of millions of cleaner fish to the system. This makes humane sea lice management a significant opportunity for welfare improvement across these species. Developing humane alternatives now could prevent expansion of harmful methods and improve welfare for millions of additional fish.

Acknowledgements

This report is a project of Rethink Priorities—a think-and-do tank dedicated to informing decisions made by high-impact organizations and funders across various cause areas. Hannah McKay did the academic and gray literature review and wrote the report. Sagar Shah oversaw the project. Thanks to Sophie Williamson and Shannon Davis for feedback, Shane Coburn for copyediting, and Urszula Zarosa for assistance with publishing the report online and dissemination.

Bibliography

Abolofia, J., Asche, F., & Wilen, J. E. (2017). The cost of lice: Quantifying the impacts of parasitic sea lice on farmed salmon. Marine Resource Economics, 32(3), 329–349. https://doi.org/10.1086/691981

Austry, D., A. (2022). Cleaner Fish—The millions of hidden casualties of the salmon industry. Conservative Animal Welfare Foundation. https://www.conservativeanimalwelfarefoundation.org/wp-content/uploads/2022/05/CAWF-Cleaner-Fish-Report-Final-.pdf, archived at https://perma.cc/HL3K-RSP3

Barrett, L. T., Overton, K., Stien, L. H., Oppedal, F., & Dempster, T. (2020). Effect of cleaner fish on sea lice in Norwegian salmon aquaculture: A national scale data analysis. International Journal for Parasitology, 50(10–11), 787–796. https://doi.org/10.1016/j.ijpara.2019.12.005

Benchmark Animal Health & Nofima. (2021). A deep dive into the cost of sea lice. Benchmark Animal Health. https://www.bmkanimalhealth.com/a-deep-dive-into-the-cost-of-sea-lice/, archived at https://perma.cc/M3RW-X9EZ

Blue lice. (n.d.). Blue Lice. Retrieved 10 November 2025, from https://www.bluelice.no

Borchel, A., & Nilsen, F. (2025). A review of the salmon louse (Lepeophtheirus salmonis) hyposalinity responses and the efficacy of freshwater delousing. Reviews in Fisheries Science & Aquaculture, 1–12. https://doi.org/10.1080/23308249.2025.2536316

Brown, A. R., Wilson, R. W., & Tyler, C. R. (2025). Assessing the benefits and challenges of recirculating aquaculture systems (RAS) for Atlantic salmon production. Reviews in Fisheries Science & Aquaculture, 33(3), 380–401. https://doi.org/10.1080/23308249.2024.2433581

Bui, S., Geitung, L., Oppedal, F., & Barrett, L. T. (2020). Salmon lice survive the straight shooter: A commercial scale sea cage trial of laser delousing. Preventive Veterinary Medicine, 181, 105063. https://doi.org/10.1016/j.prevetmed.2020.105063

Bui, S., Madaro, A., Nilsson, J., Fjelldal, P. G., Iversen, M. H., Brinchman, M. F., Venås, B., Schrøder, M. B., & Stien, L. H. (2022). Warm water treatment increased mortality risk in salmon. Veterinary and Animal Science, 17, 100265. https://doi.org/10.1016/j.vas.2022.100265

Cermaq. (2023). Cermaq Norway uses laser against salmon lice. Cermaq Global. https://www.cermaq.com/news/cermaq-norway-uses-laser-against-salmon-lice, archived at https://perma.cc/S8R3-RF5U

Geitung, L., Oppedal, F., Stien, L. H., Dempster, T., Karlsbakk, E., Nola, V., & Wright, D. W. (2019). Snorkel sea-cage technology decreases salmon louse infestation by 75% in a full-cycle commercial test. International Journal for Parasitology, 49(11), 843–846. https://doi.org/10.1016/j.ijpara.2019.06.003

Global Salmon Initiative. (2024). 2024 Sustainability Report: Data deep dive. Global Salmon Initiative. https://globalsalmoninitiative.org/en/our-progress/sustainability-report/data-deep-dive/, archived at https://perma.cc/8DPM-27DE

Grøntvedt, R. N., Nerbøvik, I.-K. G., Viljugrein, H., Lillehaug, A., Nilsen, H., & Gjevre, A.-G. (2015). Thermal de-licing of salmonid fish—Documentation of fish welfare and effect (No. 13). Veterinærinstituttet (Norwegian Veterinary Institute). https://www.vetinst.no/rapporter-og-publikasjoner/rapporter/2015/thermal-de-licing-of-salmonid-fish-documentation-of-fish-welfare-and-effect/_/attachment/inline/3130da85-cba1-4773-8e2e-8dc9d89fe2d1:51e2b38493e6fde1e5340541b9053b00d6e909dd/Report%2013_15%20-%20Thermal%20de-licing%20of%20salmonid%20fish%20-%20documentation%20of%20fish%20welfare%20and%20effect%20-%20english.pdf, archived at https://perma.cc/Z6RC-9ZV3

Imsland, A. K., Reynolds, P., Eliassen, G., Hangstad, T. A., Nytrø, A. V., Foss, A., Vikingstad, E., & Elvegård, T. A. (2014). Notes on the behaviour of lumpfish in sea pens with and without Atlantic salmon present. Journal of Ethology, 32(2), 117–122. https://doi.org/10.1007/s10164-014-0397-1

Jónsdóttir, K. E., Misund, A. U., Sunde, L. M., Schrøder, M. B., & Volent, Z. (2023). Lice shielding skirts through the decade: Efficiency, environmental interactions, and rearing challenges. Aquaculture, 562, 738817. https://doi.org/10.1016/j.aquaculture.2022.738817

Mattilsynet (Norwegian Food Safety Authority). (2023, June 1). Vær varsom med ferskvannsbehandling. Mattilsynet (Norwegian Food Safety Authority). https://www.mattilsynet.no/fisk-og-akvakultur/fiskesykdommer/lakselus/vaer-varsom-med-ferskvannsbehandling archived at https://perma.cc/53A2-5VEL

Moldal, T., Wiik-Nielsen, J., Oliveira, V. H. S., Svendsen, J., & Sommerset, I. (2025). Norwegian fish health report 2024 (No. 1b/2025). Veterinærinstituttet (Norwegian Veterinary Institute). https://www.vetinst.no/rapporter-og-publikasjoner/rapporter/2025/norwegian-fish-health-report-2024/_/attachment/inline/6b11b72c-ee8f-4529-921f-1a3d85dc419e:2d59843d7c1e34e9200669ae47f2974d8ee51b6a/Fish%20Health%20Report%202024.pdf, archived at https://perma.cc/UHY8-RNR4

Moore, G. (2025, September 22). Mowi Scotland is upping wrasse cleaner fish production by a third. https://www.fishfarmingexpert.com/ballan-wrasse-cleaner-fish-lumpfish/mowi-scotland-is-upping-wrasse-cleaner-fish-production-by-a-third/1996268, archived at https://perma.cc/E253-SNX6

Nilsson, J., Moltumyr, L., Madaro, A., Kristiansen, T. S., Gåsnes, S. K., Mejdell, C. M., Gismervik, K., & Stien, L. H. (2019). Sudden exposure to warm water causes instant behavioural responses indicative of nociception or pain in Atlantic salmon. Veterinary and Animal Science, 8, 100076. https://doi.org/10.1016/j.vas.2019.100076

Nordlaks. (n.d.). Salmon lice laser number 1000 installed at Nordlaks. Nordlaks. Retrieved 10 November 2025, from https://nordlaks.com/salmon-lice-laser-number-1000-installed-at-nordlaks/, archived at https://perma.cc/RT9M-DXZK

Optilice^TM. (n.d.). Optimar. Retrieved 19 November 2025, from https://optimarglobal.com/en/machines/fish-health/optilice

Overton, K., Barrett, L., Oppedal, F., Kristiansen, T., & Dempster, T. (2020). Sea lice removal by cleaner fish in salmon aquaculture: A review of the evidence base. Aquaculture Environment Interactions, 12, 31–44. https://doi.org/10.3354/aei00345

Overton, K., Dempster, T., Oppedal, F., Kristiansen, T. S., Gismervik, K., & Stien, L. H. (2019). Salmon lice treatments and salmon mortality in Norwegian aquaculture: A review. Reviews in Aquaculture, 11(4), 1398–1417. https://doi.org/10.1111/raq.12299

Pérez, C. (2018, November 30). A clean break for Chilean aquaculture. The Fish Site. https://thefishsite.com/articles/a-clean-break-for-chilean-aquaculture, archived at https://perma.cc/2TUF-9Y85

Powell, A., Treasurer, J. W., Pooley, C. L., Keay, A. J., Lloyd, R., Imsland, A. K., & Garcia De Leaniz, C. (2018). Use of lumpfish for sea‐lice control in salmon farming: Challenges and opportunities. Reviews in Aquaculture, 10(3), 683–702. https://doi.org/10.1111/raq.12194

Ringstad, N. K., Stormoen, M., Midtlyng, P. J., & Persson, D. (2025). Classification of post‐delousing mortality in farmed atlantic salmon: A case study of standardised causal classification at fish‐level. Journal of Fish Diseases, 48(5), e14087. https://doi.org/10.1111/jfd.14087

SalmonBusiness. (2024a, August 28). Lice explosion sees producer threatened with fine of £55,000 per day. SalmonBusiness. https://www.salmonbusiness.com/lice-explosions-sees-producer-threatened-with-a-fine-of-55000-per-day/, archived at https://perma.cc/G224-WTMW

SalmonBusiness. (2024b, October 2). SalMar to cease production of cleaner fish in anticipation of crackdown. SalmonBusiness. https://www.salmonbusiness.com/salmar-to-cease-production-of-cleaner-fish/ archived at https://www.salmonbusiness.com/salmar-to-cease-production-of-cleaner-fish/, archived at https://perma.cc/8PM5-Q2X6

Scottish Government. (2024). Scottish Fish Farm Production Survey 2023. Cabinet Secretary for Rural Affairs, Land Reform and Islands. https://www.gov.scot/publications/scottish-fish-farm-production-survey-2023/pages/6/, archived at https://perma.cc/PJ7R-Q7Z6

Sommerset, I., Bang Jensen, B., Bornø, B., Haukaas, A., & Brun, E. (2021). The Health Situation in Norwegian Aquaculture 2020 (No. 41a/2021). Veterinærinstituttet (Norwegian Veterinary Institute). https://www.vetinst.no/rapporter-og-publikasjoner/rapporter/2021/fish-health-report-2020/_/attachment/inline/d2c81a9f-2126-488c-828b-10285c988997:187b69c8c0e3ff3065bb49c49462de2e9d0c1cae/rl2230-fiskehelse-eng-3.pdf, archived at https://perma.cc/ART8-9WN9

Sommerset, I., Walde, C. S., Bang Jensen, B., Wiik-Nielsen, J., Bornø, G., Oliveira, V. H. S., Haukaas, A., & Brun, E. (2022). Norwegian Fish Health Report 2021 (No. 2a/2022). Veterinærinstituttet (Norwegian Veterinary Institute). https://www.vetinst.no/rapporter-og-publikasjoner/rapporter/2022/fish-health-report-2021/_/attachment/inline/3a529735-e485-4bf7-b05b-5677a46b6b09:31cb9146509882b4dc2c60dc915a1be6195ae015/Norwegian%20Fish%20Health%20Report%202021.pdf, archived at https://perma.cc/DX88-JRF7

Sommerset, I., Walde, C. S., Bang Jensen, B., Bornø, B., Haukaas, A., & Brun, E. (2020). The Health Situation in Norwegian Aquaculture 2019 (No. 5b/2020). Veterinærinstituttet (Norwegian Veterinary Institute). https://www.vetinst.no/rapporter-og-publikasjoner/rapporter/2020/fish-health-report-2019/_/attachment/inline/7507c5b2-df54-4028-aee8-da5ae3010d0d:728b5711c9fb60a0ba16803064780727f5bc3b6b/Fish%20health%20report%202019.pdf, archived at https://perma.cc/GFG8-WVFT

Sommerset, I., Wiik-Nielsen , J., Moldal, T., Oliveira, V. H. S., Svendsen, J. C., Haukaas, A., & Brun, E. (2024). Norwegian Fish Health Report 2023 (No. 8b/2024). Veterinærinstituttet (Norwegian Veterinary Institute). https://www.vetinst.no/rapporter-og-publikasjoner/rapporter/2024/fishhealthreport-2023/_/attachment/inline/bb455bc6-1daa-4f9e-b855-e07ed1274663:889eac6a944fd63d13ed5b4d6dfac01cae645d39/FHR%202023%20Engelsk%20utgave_web.pdf, archived at https://perma.cc/7UJF-XDBY

Stien, L. H., Lind, M. B., Oppedal, F., Wright, D. W., & Seternes, T. (2018). Skirts on salmon production cages reduced salmon lice infestations without affecting fish welfare. Aquaculture, 490, 281–287. https://doi.org/10.1016/j.aquaculture.2018.02.045

Stige, L. C., Colquhoun, D. J., & Oliveira, V. H. S. (2025). Associations between delousing practices and pasteurellosis in farmed Atlantic salmon. Journal of Fish Diseases, 48(5), e14085. https://doi.org/10.1111/jfd.14085

Stingray Marine Solutions AS. (n.d.). Stingray Marine Solutions. Retrieved 10 November 2025, from https://www.stingray.no/

Stirling Aquaculture. (2015). Technical Considerations of closed containment sea pen production for some life stages of salmonid. The Institute of Aquaculture, University of Stirling. https://dspace.stir.ac.uk/retrieve/e181cba1-f1f3-47b8-9eba-401933cbe8fc/SARFSP011_Published.pdf, archived at https://perma.cc/D2YQ-CQYX

Stranden, A. L. (2020, January 31). Every year, 50 million cleaner fish die in Norwegian fish farms (N. Bazilchuk, Trans.). Sciencenorway.No; sciencenorway.no. https://www.sciencenorway.no/animal-welfare-fish-farming-salmon-industry/every-year-50-million-cleaner-fish-die-in-norwegian-fish-farms/1631228 archived at https://www.sciencenorway.no/animal-welfare-fish-farming-salmon-industry/every-year-50-million-cleaner-fish-die-in-norwegian-fish-farms/1631228, archived at https://perma.cc/8Q7Z-M67C

Thermolicer®. (n.d.). Scale Aquaculture. Retrieved 19 November 2025, from https://scaleaq.com/product/thermolicer/ archived at https://perma.cc/QL7N-DFY5

Thompson, C., Madaro, A., Oppedal, F., Stien, L. H., & Bui, S. (2023). Delousing efficacy and physiological impacts on Atlantic salmon of freshwater and hyposaline bath treatments. Havforskningsinstituttet. https://www.hi.no/hi/nettrapporter/rapport-fra-havforskningen-en-2023-11 archived at https://perma.cc/5PAP-BXD4

Thompson, C. R. S., Madaro, A., Nilsson, J., Stien, L. H., Oppedal, F., Øverli, Ø., Korzan, W. J., & Bui, S. (2024). Comparison of non-medicinal delousing strategies for parasite (Lepeophtheirus salmonis) removal efficacy and welfare impact on Atlantic salmon (Salmo salar) hosts. Aquaculture International, 32(1), 383–411. https://doi.org/10.1007/s10499-023-01167-8

Tiedemann, I. (2024, October 30). The innovative solutions being used to tackle sea lice on salmon farms. The Fish Site. https://thefishsite.com/articles/the-innovative-solutions-being-used-to-tackle-sea-lice-on-salmon-farms, archived at https://perma.cc/GK3H-XHXA

Van Den Boogaart, L., Slabbekoorn, H., & Scherer, L. (2023). Prioritization of fish welfare issues in European salmonid aquaculture using the Delphi method. Aquaculture, 572, 739557. https://doi.org/10.1016/j.aquaculture.2023.739557

Welfare Footprint Institute. (2025). The Life of Juvenile Salmon. Welfare Footprint Institute. https://welfarefootprint.org/salmon-welfare-2/, archived at https://perma.cc/H7P9-SZJD

1. van den Boogaart et al. (2023) ↑
2. Abolofie & Wilen (2017) ↑
3. Benchmark Animal Health & Nofima, (2021). Equates to over $600 million USD ↑
4. Small species like lumpfish and wrasse that eat lice directly from salmon ↑
5. Stien et al. (2018) ↑
6. Geitung et al. (2019) ↑
7. See footnote 5 ↑
8. Jónsdóttir et al. (2023) ↑
9. See footnote 8 ↑
10. Combination treatments means either using two methods simultaneously using two methods separately but in the same week (see Moldal et al., 2025, Table 9.1.2). ↑
11. Since sea lice are adapted to marine waters, bathing salmon in freshwater can cause sea lice to detach. ↑
12. Grøntvedt et al. (2015); Overton et al. (2019) ↑
13. E.g., Thermolicer, Optilice ↑
14. Nilsson et al. (2019) ↑
15. Bui et al. (2022) ↑
16. Stige et al. (2025) ↑
17. Ringstad et al. (2025) ↑
18. Moldal et al. (2025, p. 74) ↑
19. See footnote 18 ↑
20. Moldal et al. (2025, p. 85) ↑
21. Thompson et al. (2023); Thompson et al. (2024) ↑
22. Thompson et al. (2023); Thompson et al. (2024); Borchel & Nilsen (2025, p.8) ↑
23. Mattilsynet (Norwegian Food Safety Authority) (2023) ↑
24. Austry (2022, p. 15) ↑
25. Powell et al. (2018) ↑
26. SalmonBusiness (2024b) ↑
27. Stranden (2020) ↑
28. See footnote 25 ↑
29. Overton et al. (2020); Barrett et al. (2020) ↑
30. Imsland et al. (2014) ↑
31. We briefly reviewed five major certification schemes: RSPCA Assured, Global Animal Partnership (GAP), GlobalGAP, Best Aquaculture Practices (BAP), and Aquaculture Stewardship Council (ASC). It is possible we missed information due to the speed of review required. ↑
32. Bui et al. (2020) ↑
33. RAS systems typically source seawater from approximately 25 meters below the surface, avoiding the warmer surface layers where sea lice larvae are normally found (Stirling Aquaculture, 2015; Brown et al., 2025) ↑
34. The Welfare Footprint Institute’s upcoming book on juvenile salmon welfare in RAS considers some of the welfare challenges associated with RAS farming, though it is focused on the early life stages rather than sea-water phases where lice infestations typically occur. ↑