Aquaculture-driven evolution: distribution of pyrethroid resistance in the salmon louse throughout the North Atlantic in the years 2000–2017

Helene Børretzen Fjørtoft,Ann-Kristin Tveten,Per Gunnar Espedal,Anne Stene,Vidar Teis Aspehaug,Frank Nilsen,Francois Besnier,Kevin Alan Glover,Pål Arne Bjørn,Ian Bradbury

doi:10.1093/icesjms/fsaa062

Abstract

Abstract The parasitic salmon louse, and its documented resistance to chemotherapeutants, represents the most persistent environmental challenge to global salmonid aquaculture. We used a genetic marker associated with pyrethroid resistance to analyse ∼15 000 lice collected from the North Atlantic in the period 2000–2017. The genotype associated with resistance was not detected in lice collected from throughout the North Atlantic in the year 2000 or 2002. However, by the year 2009 onwards, it was found in lice from fish farms throughout much of the North Atlantic. It was also found in modest frequencies in lice collected from wild Atlantic salmon captured off Greenland. The most recent samples displayed very high frequencies of the genotype associated with resistance, particularly in intensive aquaculture regions of Norway (&gt;90%) and Scotland (&gt;70%). These results closely align with observations from the field. We suggest that pyrethroid resistance first emerged in Europe just before or around the year 2000 and was thereafter dispersed throughout much of the North Atlantic where its increased frequency was driven by extensive pyrethroid use. Although the resistant genotype was not detected in lice from Canada, it is likely to occur in very low frequencies that would quickly increase if pyrethroids were to be used in that region.

Highlights

All food producing systems are challenged by organisms that slow down or suppress production
The study is based on the following two components: (i) a spatial–temporal analysis of pyrethroid resistance in 1462 lice collected from the North Atlantic in the period 2000–2017 to investigate resistance dispersal in the pan-Atlantic salmon louse population and (ii) a high-resolution analysis of pyrethroid resistance of >11 000 lice collected from commercial fish farms in Norway (2012–2015) and of >3500 lice collected from fish farms in Scotland (2014–2017) to investigate how resistance disperses locally under selection
The resistant genotype was not detected in salmon lice sampled from wild Russian Atlantic salmon or farmed salmon in Norway in 2000, nor in lice sampled from fish farms in Canada, Scotland, Aquaculture-driven evolution and Norway in 2002 (Figure 1)

Summary

Introduction

All food producing systems are challenged by organisms that slow down or suppress production. When pests or parasites develop resistance to chemotherapeutants, consequences can be severe for food production and security (Clark and Yamaguchi, 2001). The salmon louse is an endemic ectoparasitic copepod in the North Atlantic and Pacific, specializing on salmonids

Methods

Results

Conclusion