Salmon lice survive the straight shooter: A commercial scale sea cage trial of laser delousing

Samantha Bui,Lena Geitung,Frode Oppedal,Luke T Barrett

doi:10.1016/j.prevetmed.2020.105063

Samantha Bui, Lena Geitung + Show 2 more

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https://doi.org/10.1016/j.prevetmed.2020.105063

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Abstract

Ectoparasitic salmon louse (Lepeophtheirus salmonis) infestations are costly for Atlantic salmon (Salmo salar) farmers in Norway. As a result, there is a strong desire for solutions to prevent and control infestations, and new technologies are typically developed and commercialised rapidly, without rigorous validation. Here, we tested the efficacy of a new commercially available control measure—delousing by underwater lasers—using a replicated design at full commercial scale. Laser delousing was used in combination with a preventive method (snorkel cages), with laser nodes deployed in 3 of the 6 sea cages at the site. The trial ran for 54 days, after which time there was no difference in infestation density of mobile salmon louse stages (pre-adult, adult male or adult female) in cages with or without laser nodes installed. By the end of the trial, adult female lice numbers in all cages were close to the legislated trigger for mandatory delousing (0.5 adult female lice per fish). The laser nodes delivered a large number of pulses relative to the number of lice in the cages, indicating that a lack of lethality rather than a lack of target detection was the limiting factor. If all pulses had been effective, they should have removed between 4–38 % of mobile lice each day. There was no effect on salmon welfare indicators such as skin condition or eye status. Our results highlight the importance of rigorous validation of new technologies across a range of conditions before widespread implementation by industry.

Highlights

Aquaculture is a relatively young industry compared to terrestrial production systems (Nash, 2011), with systematic research and development only becoming a key focus since the 1970s (Kumar and Engle, 2016)
Ectoparasitic salmon louse (Lepeophtheirus salmonis) infestations are costly for Atlantic salmon (Salmo salar) farmers in Norway
Laser delousing was used in combination with a preventive method, with laser nodes deployed in 3 of the 6 sea cages at the site

Summary

Introduction

Aquaculture is a relatively young industry compared to terrestrial production systems (Nash, 2011), with systematic research and development only becoming a key focus since the 1970s (Kumar and Engle, 2016). Commercial production of finfish has become a highly lucrative industrial process analogous to modern agriculture (Asche et al, 2018; Ashche, 2008), with rapid technological advances facilitating substantial productivity growth in recent decades (Asche et al, 2018). The farming of Atlantic salmon (Salmo salar) is a shining example of rapid industry growth, with commercial production initiated only ∼50 years ago. There has been substantial focus on prevention and control of lice in aquaculture, to reduce environmental and welfare impacts of infestations on both wild and farmed salmonids (Costello, 2009; Heuch et al, 2005; Krkosek et al, 2007; McVicar, 2004; Overton et al, 2018; Thorstad et al, 2015; Torrissen et al, 2013)

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