Sensitivity assessment to azamethiphos by time-to-response bioassay and biomarkers in the sea louse Caligus rogercresseyi

Abstract

Delousing drugs have been intensively applied to salmon farming as the main method to control lice infestations. Hence, early detection of changes in the susceptibility status is crucial to control and prevent the spread of drug resistance. This study aimed to assess the sensitivity to azamethiphos in the sea louse based on the time-to-response method coupled with gene biomarkers related to drug response (ET50-PCR). Four populations of the sea lice C. rogercresseyi with contrasting sensitivity to azamethiphos drug were used to validate this assay. For those populations, EC50 and ET50 indexes were tested. Additionally, the transcription expression of 20 candidate genes related to drug response were also evaluated. Lower ET50 indexes were observed for susceptible lice populations compared with resistant ones. Moreover, gene expression analysis evidenced three genes: cytochrome p450, long non-coding RNAs 8967 and 532, as good candidate biomarkers for drug sensitivity testing. The study provides novel knowledge to assess delousing drug sensitivity by ET50-PCR bioassay in Chilean salmonid farms.