The protective effect of the Phe362Tyr mutation in salmon lice’ (Lepeophtheirus salmonis) AChE when exposed to full-scale azamethiphos bath treatments

Organophosphates are applied for medicinal bath treatments of salmon lice (Lepeophtheirus salmonis) infested farmed salmonids. This chemical class remains important despite the development of resistant parasites, due to few available treatment options. The protective effect of the Phe362Tyr mutation in one of the acetylcholinesterase (AChE) genes of L. salmonis has previously been studied in small-scale treatments with the organophosphate azamethiphos. The current study was aimed at investigating the protective effect of this mutation in field treatments of commercial fish farms. In addition the effect of different methods of sampling on the occurrence of salmon lice with zero, one or two copies of Phe362Tyr (homozygote sensitive (SS), heterozygote (RS) and homozygote resistance (RR) respectively) were investigated.