Detachment and re-attachment of Salmon lice during full-scale delousing operations on Salmon farms

This study examined salmon lice (Lepeophtheirus salmonis) numbers during different full-scale lice treatments of salmon, with focus on detachment during crowding and re-attachment post-treatment. Data was collected from 259 non-medicinal treatments (NMM) during 2018 and 2019. The dataset included da...

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Bibliographic Details
Published in:Aquaculture 2025-01, Vol.594, p.741372, Article 741372
Main Authors: Guttu, Maria, Båtnes, Anna S., Aunsmo, Arnfinn, Bjørnland, Thea, Olsen, Yngvar
Format: Article
Language:English
Subjects:
Crowding
Lepeophtheirus salmonis
Non-medicinal methods
Re-attachment
Salmo salar
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Summary:This study examined salmon lice (Lepeophtheirus salmonis) numbers during different full-scale lice treatments of salmon, with focus on detachment during crowding and re-attachment post-treatment. Data was collected from 259 non-medicinal treatments (NMM) during 2018 and 2019. The dataset included data from thermal (Optilicer), mechanical (Flatsetsund Engineering, SkaMik, Hydrolicer) and freshwater treatments. Salmon lice were counted by the staff at the aquaculture sites, and registered in the following categories: sessile, preadult/adult male (PA/AM) and adult female. A counting protocol was established in collaboration with staff from the aquaculture companies taking part, where the time for counting the parasitic salmon lice was: Sample 0: before crowding; Sample 1: at the end of the first crowding; Sample 2: during unloading of the salmon after treatment; and Sample 3: after delousing of the salmon, in the net pen. In addition to the treatments registered directly according to the protocol, we retrieved data for additional treatments directly from the aquaculture companies' own registration system. The objectives of this observational study was (1) investigate whether salmon lice detach during crowding before an NMM; (2) investigate the effect of NMM; and (3) investigate possible re-attachment after delousing. We observed an overall trend of a reduction of salmon lice numbers, with a median percentage decrease of 22% for PA/AM and 29% for adult female lice during crowding. A likely explanation for these observations is that lice detach from the salmon due to mechanical action associated with the increased density of crowding. One-sided Wilcoxon tests corroborated the hypothesis of a reduction in lice counts during crowding for PA/AM and adult female lice (p 
ISSN:0044-8486
DOI:10.1016/j.aquaculture.2024.741372