Othercited by the Tayebat archivefull text checked A-FSH-16 in-depth review

Sea lice resistant to treatment (Canada)

Salmon lice in the Pacific Ocean show evidence of evolved resistance to parasiticide treatment.

Overview

Godwin SC et al.. Sci Rep 2022 · PMID 35347162 · DOI 10.1038/s41598-022-07464-1

Pacific salmon lice have become much less sensitive to emamectin since 2010.

Does the study support the specific claim? Yes · Methodological quality: moderate

Original publication

Plain-language summary

Study explained simply

What did the researchers want to find out?: Test lice resistance.
How was the study done?: Bioassays.
How many people, animals or samples were studied?: 34 bioassays from 11 farms; 73 treatments (2010-2021).
What was actually found?: Lice needed up to 5-16 times more drug to be killed in 2021 than in 2010; after 2019, 41% of treatments left more than half of the lice.
What do the results mean in everyday life?: Treatment works less.
What are the study's limitations?: One region.
What does it say about Elawady's specific claim?: Supports.
Do the results apply to Germany and Europe?: Low.
What can explicitly not be concluded from this study?: Anything about drug residues in salmon or risk to consumers.

Scientific in-depth review

1. Full reference

Authors: Godwin SC, Bateman AW, Kuparinen A, Johnson R, Powell J, Speck K, Hutchings JA
Journal: Sci Rep
Year: 2022
Identifier: PMID 35347162 DOI 10.1038/s41598-022-07464-1 · PMC8960799
Verification: verified – PubMed E-utilities efetch, 2026-10-25
Retracted: no
Corrections: none
Extent checked: full text
Conflicts of interest and funding: Funding: Liber Ero Postdoctoral Fellowship, NSERC Discovery Grants (RGPIN-2021-04372, RGPIN-2015-04249), European Research Council (COMPLEX-FISH 770884), Academy of Finland (317495). Authors declare no competing interests. Data provided by MOWI Canada West and Cermaq to three First Nations under IMIP Framework Agreements; data and code openly available (zenodo 10.5281/zenodo.6341974).

2. Research question

Have salmon lice (Lepeophtheirus salmonis) in the Pacific (Broughton Archipelago, BC) evolved resistance to emamectin benzoate (EMB)?

3. Study design and population

Study design: Other – Retrospective analysis of industry surveillance data: EMB bioassays (EC50 via GLMMs) and farm louse counts before/after EMB treatment (hurdle models), with AICc model selection
Population: Salmon lice collected from Atlantic salmon farms in the Broughton Archipelago, British Columbia (11 farms with bioassays; all BA farms for treatment data)
Country: Canada (British Columbia)
Period: October 2010 to November 2021
Sample size: 34 bioassays from 11 farms (about 10 lice per dish, about 4 replicates per sex per bioassay); 73 of 88 EMB treatments with calculable relative post-treatment counts
Inclusion and exclusion criteria: Bioassays performed by BC Centre for Aquatic Health Sciences; treatments excluded if a non-EMB treatment followed within 3 months or counts were missing; 22 non-EMB treatments (since 2019) excluded

4. Methods and endpoints

Exposure / intervention: Calendar time; previous EMB treatment of the farm stock
Comparator: Null models assuming constant EMB sensitivity; earlier bioassays (2010)
Endpoints: EC50 of EMB in bioassays (by sex); relative post-treatment louse counts (count 3 months after / 1 month before treatment)
Statistical methods: Per-bioassay logistic GLMMs (random dish intercept) for EC50; gamma GLMs and binomial/gamma hurdle models with linear/quadratic time; AICc model selection; no farm effect (small sample)

5. Actual results

Results: Highest EC50 in July 2021: 907 (95% CI 744-1189) ppb for males and 840 (695-1073) ppb for females, a 5-fold (males) and 16-fold (females) increase vs the 2010 bioassay at the same farm; best model had quadratic time effect, 0% Akaike weight for constant sensitivity; previous treatment increased EC50 by factor 1.23 (0.95-1.59). Field efficacy: before 2019 post-treatment counts were 8.6% +/- 1.6% of pre-treatment counts and 1/56 relative counts >0.5; 2019-2021: 7/17 (41%) >0.5; three 2021 treatments resulted in higher counts post-treatment (treatment failure). 2021 EC50 values comparable to or higher than resistant Atlantic Canada strains. Non-EMB treatments made up 62% of treatments in 2021.
Absolute risks: not applicable (parasite resistance; no human outcome)
Authors' conclusion: Salmon lice in the Pacific have recently evolved substantial resistance to EMB; outbreaks on Pacific farms will be harder to control; resistance may stem from depleted wild salmon, reliance on a single treatment or insufficient treatment, suggesting management failure.

6. Strengths

Two independent lines of evidence (bioassays and field efficacy)
Raw data and code openly available
Model selection transparent (AICc values reported)
Authors note data access via Indigenous-led agreements

7. Weaknesses

One region (11 farms), small number of bioassays (34)
No genetic confirmation of resistance (lice not retained)
Louse counts performed by farm staff; no farm random effect
Confounding of field efficacy by environmental conditions and treatment practices not modelled
Says nothing about EMB residues in sediment, seabed crustaceans or human consumers

8. Risk of bias

Orienting tool: No standard tool fits (ecological/surveillance data analysis); structured validity judgement
Type of assessment: structured assessment based on the full text by a single reviewer (no formal double review)
Full formal assessment: no
Overall risk of bias: some concerns
Rationale: Single-reviewer structured judgement based on the full text; not formal (would need two independent reviewers). Changed from low to some_concerns because of small, single-region industry data without genetic confirmation.

8. Risk of bias
Domain	Judgement	Rationale
Data source and selection	some concerns	Industry-collected bioassays and counts from one region; non-random timing of bioassays (performed when variation suspected).
Measurement	low	Standard CAHS bioassay protocol; EC50 estimated with CIs.
Confounding / alternative explanations	some concerns	Farm, temperature and treatment execution not modelled; no genetic data; but bioassay and field trends concordant.
Analysis and reporting	low	Pre-defined model sets with AICc; open data and code.

Full-text review (25 October 2026): Added n (34 bioassays/11 farms; 73 treatments), period 2010-2021, EC50 values with CIs (907/840 ppb; 5- and 16-fold), field-efficacy numbers, funding, open data; noted no genetic confirmation and scope limited to resistance; bias overall changed from low to some_concerns.

9. Assessment of the statistical interpretation

Trend inference rests on 34 bioassays and 73 treatments; the strongest increase is driven by 2021 values (quadratic time). Model support for change over time is strong (null models 0% Akaike weight).

10. Relevance to the specific claim

C-FSH-10.

11. Independent contrary findings

12. Transferability to Germany and Europe

Not directly.

13. Overall methodological judgement

Credible evidence of emerging EMB resistance in Pacific salmon lice in one Canadian region. Supports only the resistance part of C-FSH-10; it does not address the Scottish sediment (97%) or seabed-crustacean statements, nor any consumer health risk.

Multidimensional assessment
Multidimensional assessment
Authenticity of the source	verified
Methodological quality	moderate
Risk of bias	some concerns
Precision of results	low
Directness	very indirect
Reproducibility	unknown
Consistency with the overall evidence	consistent
Regional transferability	low
Adequacy of the interpretation (by the archive)	essentially correct but incomplete

14. Open questions

Genetic confirmation; other Pacific regions; environmental EMB levels.

15. Linked fact checks

The sea-lice drug emamectin benzoate was found in 97% of sediment samples around Scottish salmon farms and harmed seabed crustaceans, and sea lice in the Pacific have evolved resistance to it. – Studies supporting the claim

Use by the Tayebat archive

Note: according to the archive, the studies were compiled by the archive operators. Whether Dr. Elawady himself cited this study is not established.

What the archive says about the study: Bibliography; narrative attributes it to 'Bateman' (first author is Godwin SC; Bateman AW second author).
A. What was actually studied?: Lice resistance.
B. What did the authors find?: EC50 rose 5-fold (males) and 16-fold (females) 2010-2021 at the same farm; field efficacy fell (41% of treatments 2019-2021 left >50% of lice).
C. What conclusions do the authors themselves draw?: Outbreaks harder to control.
D. What does the archive derive from it?: Supports 'pesticide use threatens ecological health'.
E. Is this derivation scientifically justified?: Correct for parasite resistance and ecological/management concern; author attribution imprecise (first author Godwin); not evidence about food safety.
Adequacy of the interpretation (by the archive): essentially correct but incomplete