Immunostimulation of Salmo salar L., and its effect on Lepeophtheirus salmonis (Krøyer) P‐glycoprotein mRNA expression following subsequent emamectin benzoate exposure

Abstract

Control of sea lice, Lepeophtheirus salmonis, on farmed Atlantic salmon, Salmo salar, relies heavily on chemotherapeutants. However, reduced efficacy of many treatments and need for integrated sea lice management plans require innovative strategies. Resistance to emamectin benzoate (EMB), a major sea lice parasiticide, has been linked with P-glycoprotein (P-gp) expression. We hypothesized that host immunostimulation would complement EMB treatment outcome. Lepeophtheirus salmonis-infected Atlantic salmon were fed immunostimulatory or control feeds. Sea lice were collected for 24-h EMB bioassays 1 and 2 weeks prior to commencement of EMB treatment of the fish. Two weeks after cessation of immunostimulant-treated feed, EMB was administered at 150 μg kg(-1) fish biomass for 7 days. The bioassay revealed stage, gender and immunostimulant-related differences in EMB EC(50) . Sea lice attached to salmon with a history of immunostimulation exhibited significantly greater survival than those on control feeds, despite similar levels of EMB in host tissues. Lepeophtheirus salmonis from salmon with a history of immunostimulation also exhibited higher P-gp mRNA expression as well as greater survivability compared to controls. Administration of immunostimulants prior to EMB treatment caused increased expression of P-gp mRNA which could have consequently caused decreased efficacy of the parasiticide.

Knockout of a P‐glycoprotein gene increases susceptibility to abamectin and emamectin benzoate in Spodoptera exigua

“…For example, increased transcript levels for PxP‐gp1 were consistently detected in abamectin‐resistant strains of P. xylostella , independently of exposure to the insecticide (Tian et al ., ). Increased gene expression of the P‐gp transporter was associated with resistance to EB in Lernaeocera salmonis (Heumann et al ., ; Igboeli et al ., ), ivermectin resistance in Caenorhabditis elegans (James & Davey, ) and abamectin resistance in D. melanogaster (Luo et al ., ). Additionally, susceptibility to abamectin in a resistant strain of Tetranychus cinnabarinus increased by 74.51% after treatment with verapamil, a specific inhibitor for P‐gp (Xu et al ., ).…”

Sea lice population and sex differences in P-glycoprotein expression and emamectin benzoate resistance on salmon farms in the Bay of Fundy, New Brunswick, Canada

“…Briefly, L. salmonis egg strings harvested from BMA 2a were hatched in‐house, yielding F1 generation (R1‐2a) nauplii, and allowed to develop to the copepodid life stage in static seawater incubators prior to exposure to naïve Atlantic salmon . Lepeophtheirus salmonis were reared to adult stage on their hosts and allowed to in‐breed to produce egg strings for a second filial generation: R2‐2a.…”

“…Briefly, L. salmonis egg strings harvested from BMA 2a were hatched in-house, yielding F1 generation (R1-2a) nauplii, and allowed to develop to the copepodid life stage in static seawater incubators prior to exposure to naïve Atlantic salmon. 8,29 Lepeophtheirus salmonis were reared to adult stage on their hosts and allowed to in-breed to produce egg strings for a second filial generation: R2-2a. S0-2b egg strings were also hatched in the laboratory and the resultant copepodids (S1-2b; 120 copepodids/fish), as well as R2-2a (50 copepodids/fish), were used to infect Atlantic salmon (200 g) separately.…”

Sexual maturation and administration of 17β-estradiol and testosterone induce complex gene expression changes in skin and increase resistance of Atlantic salmon to ectoparasite salmon louse

“…Development of biological methods for prevention and mitigation needs better understanding of host pathogen interactions and mechanisms of salmon resistance to the parasite, which may depend on multiple factors including the genetic background, nutrition, properties of skin, ability to heal wounds and the immune system responses (Wagner et al, 2008;Gharbi et al, 2009;Gjerde et al, 2011;Igboeli et al, 2013;Purcell et al, 2013). Teleost skin is a dynamic organ expressing great variability in physical properties, cell types and hormonal systems involved (reviewed by Rakers et al, 2010;Esteban, 2012).…”