Disruption of host‐seeking behaviour by the salmon louse, Lepeophtheirus salmonis, using botanically derived repellents

Abstract

The potential for developing botanically derived natural products as novel feed-through repellents for disrupting settlement of the salmon louse, Lepeophtheirus salmonis (Caligidae) upon farmed Atlantic salmon, Salmo salar, was investigated using an established laboratory vertical Y-tube behavioural bioassay for assessing copepodid behaviour. Responses to artificial sea water conditioned with the odour of salmon, or to the known salmon-derived kairomone component, α-isophorone, in admixture with selected botanical materials previously known to interfere with invertebrate arthropod host location were recorded. Materials included oils extracted from garlic, Allium sativum (Amaryllidaceae), rosemary, Rosmarinus officinalis (Lamiaceae), lavender, Lavandula angustifolia (Lamiaceae), and bog myrtle, Myrica gale (Myricaceae), and individual components (diallyl sulphide and diallyl disulphide from garlic; allyl, propyl, butyl, 4-pentenyl and 2-phenylethyl isothiocyanate from plants in the Brassica genus). Removal of attraction to salmon-conditioned water (SCW) or α-isophorone was observed when listed materials were presented at extremely low parts per trillion (ppt), that is picograms per litre or 10 level. Significant masking of attraction to SCW was observed at a level of 10 ppt for diallyl disulphide and diallyl sulphide, and allyl isothiocyanate and butyl isothiocyanate. The potential of very low concentrations of masking compounds to disrupt Le. salmonis copepodid settlement on a host fish has been demonstrated in vitro.

Prevention not cure: a review of methods to avoid sea lice infestations in salmon aquaculture

“…2013; O’Shea et al . 2017). Indeed, some existing commercially available functional feeds are claimed to reduce attraction of lice towards fish (e.g.…”

Applying genetic technologies to combat infectious diseases in aquaculture

“…Some existing commercial feeds are claimed to contain repellent semiochemical additives and European patents exist for some methods and feed compositions for masking fish semiochemicals (e.g., European Patent Number EP2517568A1). Research has shown that ectoparasite infections on fish (amberjack, Nile tilapia and rainbow trout) are reduced when the fish are grown using diets containing plant derived extracts or beta‐glucan additives 600–603 and proof‐of‐concept evidence has shown that botanically‐derived materials can be incorporated into feed additives to reduce the attraction of L. salmonis to salmonid host cues 604 . Increased knowledge about genetic differences in semiochemical production between resistant and susceptible hosts to sea lice infection may help in the design of the formulation of feed additives for use to boost Atlantic salmon's ability to resist sea lice infection.…”

A century of parasitology in fisheries and aquaculture

“…These seek the upper layers of water when attaching to the host, an observation that was exploited by Geitung et al (2019) when constructing snorkel cages to prevent copepodids from attacking salmon kept at lower water depths. Still other ideas were developed that included the use of herbal repellents to jam the parasite's host finding (O'Shea et al , 2016). Genetic markers for susceptibility have been identified (Gharbi et al , 2009), and quantitative trait loci for resistance in salmon have been described (Robledo et al , 2019), which may lead to development of breeding programmes to obtain salmon with a higher natural resistance to infection.…”