Influence of different materials on the concentration of delousing agents in sea water during bioassays

Helgesen, Kari Olli; Horsberg, Tor Einar

doi:10.1111/jfd.12046

Cited by 5 publications

(4 citation statements)

References 11 publications

(21 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…An earlier study from this laboratory detected 49.7% of a nominal EMB concentration of 200 μg L − 1 3 h after the start of exposures ( Carmichael et al, 2013 ). Similarly, in another study ( Helgesen and Horsberg, 2013b ), 48.9% of an nominal concentration of 150 μg L − 1 EMB was detected in the seawater phase at the end of 24 h salmon louse bioassays performed in high-density polyethylene dishes. In the same study, recoveries were slightly less in tests using glass dishes (41.9%) and substantially inferior when using Teflon™ or silanised glass containers (27.4% and 24.0%, respectively) ( Helgesen and Horsberg, 2013b ).…”

Section: Discussionsupporting

confidence: 53%

Time-to-response toxicity analysis as a method for drug susceptibility assessment in salmon lice

et al. 2016

View full text Add to dashboard Cite

The salmon louse Lepeophtheirus salmonis (Krøyer, 1837) is an ectoparasite causing infections of wild and farmed Atlantic salmon (Salmo salar L.) in the Northern hemisphere. While L. salmonis control at commercial mariculture sites increasingly employs non-medicinal approaches, such as cage designs reducing infection rates and biological control through cleaner fish, anti-parasitic drugs are still a requirement for effective fish health care. With only a limited range of salmon delousing agents available, all of which have been in use for more than a decade, drug resistance formation has been reported for different products. Successful resistance management requires reliable susceptibility assessment, which is usually achieved through L. salmonis bioassays. These tests involve the exposure of parasites to different drug concentrations and require significant numbers of suitable L. salmonis stages. The present study reports an alternative bioassay that is based on time-to-response toxicity analyses and can be carried out with limited parasite numbers. The assay determines the median effective time (ET50), i.e., the time required until impaired swimming and/or attachment behaviour becomes apparent in 50% of parasites, by conducting repeated examinations of test animals starting at the time point where exposure to a set drug concentration commences. This experimental approach further allows the estimation of the apparent drug susceptibility of individual L. salmonis by determining their time to response, which may prove useful in experiments designed to elucidate associations between genetic factors and the drug susceptibility phenotype of parasites. Three laboratory strains of L. salmonis differing in susceptibility to emamectin benzoate were characterised using standard 24 h bioassays and time-to-response toxicity assays. While both the median effective concentration (EC50) and the ET50 showed variability between experimental repeats, both types of bioassay consistently discriminated susceptible and drug-resistant L. salmonis laboratory strains.Statement of relevanceInfections by sea lice cause significant costs to the global salmon farming industry, which have been estimated to exceed €300 million per year worldwide. Control of sea lice still relies to a significant extent on chemical delousing; however, chemical control is threatened by resistance formation. Resistance can be combated by rotation between different drugs and strategic implementation of non-medicinal strategies. However, resistance management requires reliable and feasible methods of susceptibility assessment.The present study is a technical note introducing a novel approach to susceptibility assessments in sea lice. The method can be applied in susceptibility assessments on farms, where it offers the advantage of a reduced requirement of parasites for testing. In addition, the novel method allows deriving the times of parasite require to show a response after drug treatment has started, thus providing a variable characterizing the drug susceptibi...

show abstract

Section: Discussionsupporting

confidence: 53%

Time-to-response toxicity analysis as a method for drug susceptibility assessment in salmon lice

et al. 2016

View full text Add to dashboard Cite

show abstract

“…The measured EMB concentration in the nominal 200 μg L -1 EMB treatment was 99.5 ± 5.2 μg L -1 EMB. This depletion of solubilised active ingredient may be attributed to EMB adsorption to the glass containers used for exposure assays [53]. …”

Section: Methodsmentioning

confidence: 99%

Salmon lice (Lepeophtheirus salmonis) showing varying emamectin benzoate susceptibilities differ in neuronal acetylcholine receptor and GABA-gated chloride channel mRNA expression

et al. 2013

View full text Add to dashboard Cite

BackgroundCaligid copepods, also called sea lice, are fish ectoparasites, some species of which cause significant problems in the mariculture of salmon, where the annual cost of infection is in excess of €300 million globally. At present, caligid control on farms is mainly achieved using medicinal treatments. However, the continued use of a restricted number of medicine actives potentially favours the development of drug resistance. Here, we report transcriptional changes in a laboratory strain of the caligid Lepeophtheirus salmonis (Krøyer, 1837) that is moderately (~7-fold) resistant to the avermectin compound emamectin benzoate (EMB), a component of the anti-salmon louse agent SLICE® (Merck Animal Health).ResultsSuppression subtractive hybridisation (SSH) was used to enrich transcripts differentially expressed between EMB-resistant (PT) and drug-susceptible (S) laboratory strains of L. salmonis. SSH libraries were subjected to 454 sequencing. Further L. salmonis transcript sequences were available as expressed sequence tags (EST) from GenBank. Contiguous sequences were generated from both SSH and EST sequences and annotated. Transcriptional responses in PT and S salmon lice were investigated using custom 15 K oligonucleotide microarrays designed using the above sequence resources. In the absence of EMB exposure, 359 targets differed in transcript abundance between the two strains, these genes being enriched for functions such as calcium ion binding, chitin metabolism and muscle structure. γ-aminobutyric acid (GABA)-gated chloride channel (GABA-Cl) and neuronal acetylcholine receptor (nAChR) subunits showed significantly lower transcript levels in PT lice compared to S lice. Using RT-qPCR, the decrease in mRNA levels was estimated at ~1.4-fold for GABA-Cl and ~2.8-fold for nAChR. Salmon lice from the PT strain showed few transcriptional responses following acute exposure (1 or 3 h) to 200 μg L-1 of EMB, a drug concentration tolerated by PT lice, but toxic for S lice.ConclusionsAvermectins are believed to exert their toxicity to invertebrates through interaction with glutamate-gated and GABA-gated chloride channels. Further potential drug targets include other Cys-loop ion channels such as nAChR. The present study demonstrates decreased transcript abundances of GABA-Cl and nAChR subunits in EMB-resistant salmon lice, suggesting their involvement in avermectin toxicity in caligids.

show abstract

“…However, most of the studies reported on both the literature and presentations on the workshop use glass (Table ). This arises from the information that chemotherapeutants have different adherence to materials affecting the actual concentration to which parasites are exposed (Helgesen & Horsberg, ). It is also important to note that the material and equipment used to carry out the bioassay should reduce sea lice handling to ensure that healthy individuals are tested for sensitivity.…”

Section: Resultsmentioning

confidence: 99%

Sensitivity assessment of sea lice to chemotherapeutants: Current bioassays and best practices

Marín

Mancilla

Hausdorf³

et al. 2017

Journal of Fish Diseases

View full text Add to dashboard Cite

Traditional bioassays are still necessary to test sensitivity of sea lice species to chemotherapeutants, but the methodology applied by the different scientists has varied over time in respect to that proposed in "Sea lice resistance to chemotherapeutants: A handbook in resistance management" (2006). These divergences motivated the organization of a workshop during the Sea Lice 2016 conference "Standardization of traditional bioassay process by sharing best practices." There was an agreement by the attendants to update the handbook. The objective of this article is to provide a baseline analysis of the methodology for traditional bioassays and to identify procedures that need to be addressed to standardize the protocol. The methodology was divided into the following steps: bioassay design; material and equipment; sea lice collection, transportation and laboratory reception; preparation of dilution; parasite exposure; response evaluation; data analysis; and reporting. Information from the presentations of the workshop, and also from other studies, allowed for the identification of procedures inside a given step that need to be standardized as they were reported to be performed differently by the different working groups. Bioassay design and response evaluation were the targeted steps where more procedures need to be analysed and agreed upon.

show abstract

Influence of different materials on the concentration of delousing agents in sea water during bioassays

Cited by 5 publications

References 11 publications

Time-to-response toxicity analysis as a method for drug susceptibility assessment in salmon lice

Time-to-response toxicity analysis as a method for drug susceptibility assessment in salmon lice

Salmon lice (Lepeophtheirus salmonis) showing varying emamectin benzoate susceptibilities differ in neuronal acetylcholine receptor and GABA-gated chloride channel mRNA expression

Sensitivity assessment of sea lice to chemotherapeutants: Current bioassays and best practices

Contact Info

Product

Resources

About