Assessing heritable variation in biological control of the salmon louse by two species of cleaner fish and co-operative behaviour by their client, Atlantic salmon

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Aquaculture now produces all the Atlantic salmon consumed by Canadians as well as a significant amount for export. The salmon louse is a marine parasitic species of copepod that has a direct impact on farm income through inventory losses caused by skin and gill damage which can also increase disease risks. Levels of sea lice infestation were historically controlled using husbandry practices including area management and lower stocking densities. A limited number of chemical therapeutants have been authorized for use but sole reliance on these parasiticides can lead to sea lice resistance. The industry has now adopted an Integrated Pest Management approach to sea lice management, which uses several alternate treatment options. In Europe, cleaner fishes such as the lumpfish and European wrasses are introduced into sea cages to eat the lice off the Atlantic salmon. In eastern Canada, the lumpfish and a North American wrasse, the cunner, have been shownto significantly reduce adult lice densities on salmon living in marine sea cages. Further some families of lumpfish are more effective lice cleaners than others suggesting lice cleaning propensity is heritable. It is unknown whether co-operative behaviour by salmon (e.g., remaining stationary) to facilitate lice cleaning ever occurs in sea cages, and if so whether the behaviour is heritable. Genotyping Atlantic salmon with high density SNP (Single Nucleotide Polymorphisms) chips has revealed SNPs associated with lower lice counts in the absence of cleaner fish. Our proposal has the following objectives: 1) determine the best size-class of cunners to use to clean Atlantic salmon in commercial sea cages; 2) determine the stock structure and examine variation in lice-cleaning performance among cunners and among lumpfish from different stocks; 3) assess heritable variation in lice eating behaviour among families of cunners and of lumpfish; 4) Conduct lice challenges with and without the lice cleaner fish present to see if there is a change in the ranking of salmon families with respect to lice counts with and without the biological control agent present. Our work will reduce the economic costs of sea lice control by the Canadian Atlantic salmon industry and increase its sustainability.