An investigation into the molecular determinants of salmon louse (Lepeophtheirus salmonis (Krøyer, 1837)) susceptibility to the antiparasitic drug emamectin benzoate.

• Main Author: Carmichael, Stephen N
• Other Authors: Sturm, Armin, Bron, James, Skuce, Philip, Scottish Salmon Producers Organisation (SSPO), The Moredun Foundation
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Stirling 2013
• Subjects: drug resistance; sea lice; avermectin; ligand-gated chloride channel; cys-loop receptor; sex determination; RAD-seq; single nucleotide polymorphism; Atlantic salmon; Lepeophtheirus salmonis; Avermectins; Fishes Diseases; Salmo salar; Copepods
• Online Access: http://hdl.handle.net/1893/19526; http://dspace.stir.ac.uk/bitstream/1893/19526/1/StephenCarmichael_PhD_Thesis_Final.pdf

Caligid copepods, also called sea lice, are ectoparasites of marine fish, with Lepeophtheirus salmonis (Krøyer, 1837) emerging as a problem for mariculture of Atlantic salmon (Salmo salar Linnaeus, 1758) in the northern hemisphere. Annual costs of sea lice to global salmon farming was estimated to be in excess of €300 million in 2006, with the majority of this accounted for through expenses accrued from chemical treatments. Only a limited range of anti-sea louse drugs are available and licensed for the treatment of fish, and the continued use of only a few compounds creates a situation potentially favouring the development of drug resistance. Emamectin benzoate (EMB) is currently used as a salmon delousing agent, being employed as a 0.2 % in-feed pre-mix (SLICE®). Atlantic salmon farmers have reported increased incidence of reduced L. salmonis sensitivity to SLICE®, which has highlighted the requirement for further research into the molecular mechanisms controlling salmon louse resistance to EMB. Genomic and transcriptomic research concerning L. salmonis drug resistance mechanisms has not often been reported, with previous transcriptomic studies using candidate gene approaches and genetic studies focussing on population genetics. Drug resistance in ecdysozoan invertebrates is associated with a variety of molecular mechanisms including target site mutations and changes in the expression of components in drug detoxification pathways. The research reported in this thesis was aimed at the exploration of mechanisms employed by L. salmonis to reduce the toxicity of EMB exposure, following a transcriptomic approach that utilised custom oligonucleotide (oligo) microarrays and a genetic approach that utilised Restriction-site associated DNA sequencing (RAD-seq) to identify Single Nucleotide Polymorphism (SNP) markers. An EMB-resistant (PT) and drug-susceptible (S) L. salmonis laboratory-maintained strain were to be used as a model for this research, as these two strains differ in EMB susceptibility (~ 7-fold) and show ...