Novel tools and knowledge for a future with no lice infestations in Norwegian aquaculture

The overall aim of this project is to identify naturally produced compounds that are associated with Atlantic salmon susceptibility and resistance to two parasitic sea lice species that are of major concern because of their effects on fish welfare and to develop tools that can be applied to boost Atlantic salmon resistance and reduce lice infestation in Norway. We had previously established that there was substantial genetic variation in susceptibility to lice infestation within farmed Norwegian Atlantic salmon populations and also detected some compounds released by the skin of Atlantic salmon that were associated with this variation. However the mechanisms triggering the release of these compounds, and their underlying genetic basis was still unknown. This project identified host-specific compounds associated with susceptibility to lice parasitisation, tested whether measurement of these compounds could provide an accurate and more ethical phenotype (without challenge testing) for breeding to boost resistance, identified and tested feed additives that could potentially block production of attractant compounds or boost mucosal secretion of compounds repelling lice and tested for additional effects on the reproductive capacity of the lice and its epidemiology that might be derived from breeding for resistance. The research objectives and results of this project integrated with those of a separate research project funded by FHF, and utilised results from our previous projects, to enhance genetic improvement with selective breeding and prioritise candidate genes for manipulation via feed additives to produce salmon with full or high resistance. Outcomes included improved fundamental knowledge of lice resistance mechanisms and development of tools that can be applied to boost genetic and non-genetic resistance to sea lice.

A. Outcomes: 1. Several compounds found to inhibit or stimulate lice activity, although effects are weak 2. Differences in the semiochemical concentrations in mucus from individuals showing high versus low lice count detected and we suspect there is additive genetic variation behind these differences in semiochemical concentrations. 3. Unable to assess correlation between host-resistance mechanisms against both lice species as we were unable to source C. elongatus when it was needed for challenge testing families. 4. Unable to assess genetic variation in susceptibility of Atlantic salmon to C. elongatus for reasons given above. 5. If the overall profile is heritable, there would be a low probability of falsely identifying highly resistant fish that should be used for breeding, and biochemical phenotypes could have utility for breeding. 6. Several potential gene markers for sea lice attachment success identified, some of which could be associated with semiochemical production. 7. A suite of compounds and feed additives were identified and evaluated. 8. Although we have detected several loci containing potential markers affecting host-resistance to sea lice, we believe these will have small utility for enriching the estimation of genomic breeding values. 9. A suite of products with putative anti-lice properties were tested. The most promising result was for a phytogenic product referred to here as product. Lice behavior tests showed dose-dependent inhibitory effect of the product while testing of the product in feeds showed promising effects, including mortality and retardation of parasites’ development. The action of the product has been characterized with transcriptomic analysis and it has been shown to stimulate antigen presentation, chemokine production, interferon a, ROS producing enzymes and antiviral genes. Patent applications for the product have been filed by partner Cargill. 10. Found that lice that develop and mature on salmon that have been bred for reduced sea lice count are less infective. If we were to farm fish which are bred for low sea lice count in the future, we would expect the epidemiology of the disease would be reduced and we would see less infection of farmed and wild fish as a result of the suppression of contagion. B. Impacts: 2. Improved ability of salmon to repel lice with Cargill production and sales of the Product. 3. Reduced lice effective reproduction rate (ie. lowered lice infectivity) with breeding to reduce lice count. 4. Using both feed additives and breeding might reduce the need for delousing, but elimination of delousing is unlikely. 5. Feed additives and reduced infectivity of lice through breeding should improve fish welfare by lowering parasite epidemiology and loads in the future. This should translate into reduced need for delousing and reduced farm costs.

The overall aim of this project is to identify compounds (semiochemicals) that are associated with Atlantic salmon susceptibility and resistance to the parasitic copepodids Lepeophtheirus salmonis and Caligus elongatus and to develop tools that can be applied to boost Atlantic salmon resistance and reduce lice infestation in Norway. We have previously established that there is substantial genetic variation in susceptibility to L. salmonis within farmed Norwegian Atlantic salmon populations and also detected some compounds released by the skin of Atlantic salmon that are associated with this variation. However the mechanisms triggering the release of these compounds, and their underlying genetic basis is still unknown. This project will identify host-specific semiochemicals (kairomones that attract and/or allomones that deter lice) within the Atlantic salmon population associated with the level of lice parasitisation, test whether measurement of semiochemical production could provide an accurate and more ethical phenotype (without challenge testing) for breeding to boost resistance, identify and test feed additives that could potentially block semiochemical attractant production or boost mucosal secretion of semiochemicals repelling lice and test for additional effects on the reproductive capacity of the lice and its epidemiology that might be derived from breeding for resistance. The research objectives and results of this project will integrate with those of a separate research project funded by FHF, and utilise results from our previous projects, to enhance genomic selection and prioritise candidate genes for manipulation via feed additives to produce salmon with full or high resistance. Outcomes will include improved fundamental knowledge of lice resistance mechanisms and development of tools that can be applied to boost genetic and non-genetic resistance to sea lice.