Trends in de-lousing of Norwegian farmed salmon from 2000-2019-Consumption of medicines, salmon louse resistance and non-medicinal control methods

Overview
TitleTrends in de-lousing of Norwegian farmed salmon from 2000-2019-Consumption of medicines, salmon louse resistance and non-medicinal control methods
AuthorsMyhre Jensen E, Horsberg TE, Sevatdal S, Helgesen KO
TypeJournal Article
Journal NamePloS one
Volume15
Issue10
Year2020
Page(s)e0240894
CitationMyhre Jensen E, Horsberg TE, Sevatdal S, Helgesen KO. Trends in de-lousing of Norwegian farmed salmon from 2000-2019-Consumption of medicines, salmon louse resistance and non-medicinal control methods. PloS one. 2020; 15(10):e0240894.

Abstract

The salmon louse Lepeophtheirus salmonis has been a substantial obstacle in Norwegian farming of Atlantic salmon for decades. With a limited selection of available medicines and frequent delousing treatments, resistance has emerged among salmon lice. Surveillance of salmon louse sensitivity has been in place since 2013, and consumption of medicines has been recorded since the early 80's. The peak year for salmon lice treatments was 2015, when 5.7 times as many tonnes of salmonids were treated compared to harvested. In recent years, non-medicinal methods of delousing farmed fish have been introduced to the industry. By utilizing data on the annual consumption of medicines, annual frequency of medicinal and non-medicinal treatments, the aim of the current study was to describe the causative factors behind salmon lice sensitivity in the years 2000-2019, measured through toxicity tests-bioassays. The sensitivity data from 2000-2012 demonstrate the early emergence of resistance in salmon lice along the Norwegian coast. Reduced sensitivity towards azamethiphos, deltamethrin and emamectin benzoate was evident from 2009, 2009 and 2007, respectively. The annual variation in medicine consumption and frequency of medicinal treatments correlated well with the evolution in salmon louse sensitivity. The patterns are similar, with a relatively small response delay from the decline in the consumption of medicines in Norway (2016 and onward) to the decline in measured resistance among salmon louse (2017 and onward). 2017 was the first year in which non-medicinal treatments outnumbered medicinal delousing treatments as well as the peak year in numbers of cleanerfish deployed. This study highlights the significance of avoiding heavy reliance on a few substance groups to combat ectoparasites, this can be a potent catalyst for resistance evolution. Further, it demonstrates the importance of transparency in the global industry, which enables the industry to learn from poor choices in the past.

Author Details
Additional information about authors:
Details
1Elena Myhre Jensen
2Tor Einar Horsberg
3Sigmund Sevatdal
4Kari Olli Helgesen
Properties
Additional details for this publication include:
Property NameValue
Journal CountryUnited States
Publication TypeJournal Article
Language Abbreng
LanguageEnglish
Elocation10.1371/journal.pone.0240894
DOI10.1371/journal.pone.0240894
Journal AbbreviationPLoS One
Publication Date2020
eISSN1932-6203
ISSN1932-6203
Publication ModelElectronic-eCollection
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PMID: PMID:33119627