Resistance of sea lice, Lepeophtheirus salmonis (Krøyer), to hydrogen peroxide on farmed Atlantic salmon, Salmo salar L.

Abstract

Hydrogen peroxide has been the only medicine used to treat salmon infected with sea lice [Lepeophtheirus salmonis (Krøyer)] on many farms in Scotland since 1992 and reports have suggested reduced treatment efficacy. The present study tests the sensitivity of sea lice to exposure to hydrogen peroxide under farm conditions and also in vivo by comparing lice from a farm with suspected resistance and lice from a farm that had not been pre‐exposed to hydrogen peroxide. In bin treatments on fish from a farm treated with hydrogen peroxide on 41 occasions, numbers of ovigerous lice declined by only 15% and 16% in two replicates and other mobile stages by 25%. Where hydrogen peroxide had not been used, ovigerous females declined by 90% and 87% and other mobile lice stages by 97% and 99%. These trials and observed poor efficacy of cage treatments, for example only 7.5% reduction in lice numbers when fish were treated with 2000 p.p.m. for 20 mins, indicated resistance of lice to hydrogen peroxide. The mechanisms involved in the development of resistance, possible genetic selection for lice with reduced carapace permeability or detoxifying enzymes such as catalase, or tolerance through induction by subtherapeutic exposure are reviewed. Implications for lice control strategies relying on hydrogen peroxide are discussed.

First report of reduced sensitivity towards hydrogen peroxide found in the salmon louse Lepeophtheirus salmonis in Norway

“…Most fish farms are dependent on chemical treatments in order to keep the parasite numbers below national maximum permitted levels, but few chemical treatment agents are available (Burka et al, 1997;Roth, 2000;Westcott et al, 2004). This has subsequently led to the development of reduced sensitivity in L. salmonis towards most of the available chemical treatments (Jones et al, 1992;Lees et al, 2008a;Roth et al, 1996;Sevatdal and Horsberg, 2003;Treasurer et al, 2000). The geographical dispersion of the reduced sensitivity towards each treatment agent varies (Grøntvedt et al, 2014;Jones et al, 2013;Lees et al, 2008b).…”

Clinical efficacy of teflubenzuron (Calicide®) for the treatment of Lepeophtheirus salmonis infestations of farmed Atlantic salmon Salmo salar at low water temperatures

“…The principal chemotherapeutic agents currently used to control sea lice under commercial conditions in various countries include dichlorvos (Aquagard  , Novartis), azamethiphos (Salmosan  , Novartis), hydrogen peroxide (Paramove (Roth 2000). Reduced sensitivity to several of these products has been reported (Jones et al 1992, Treasurer et al 2000.…”

Population genetic structure of the parasitic copepod Lepeophtheirus salmonis throughout the Atlantic

“…Reduced sensitivity and/or resistance of Lepeophtheirus salmonis to medicated treatments have been documented in Atlantic populations (Jones et al 1992, Treasurer et al 2000, Tully & McFadden 2000, Sevatdal & Horsberg 2003, Fallang et al 2004, and the efficacy of treatments has decreased over time (Lees et al 2008). Therefore, a vital issue from both an evolutionary and management perspective is the dispersal of lice.…”