Forsøksdyr: Refine the existing challenge model for T. finnmarkense and T. maritimum and investigate the potential horizontal spread from lumpsucker to Atlantic salmon

Godkjenningsdato 30.08.2018

Bacterial skin infections are currently the main bacteriological problem for the Norwegian salmon farming industry due to their impact on fish welfare and economic impact. Official reports indicate that 16% of all Atlantic salmon transferred to sea in Norway are lost during the production cycle, and that a large part of these losses are due to skin lesions/ulcers. Recently, severe outbreaks of tenacibaculosis have been reported in Norway associated with significant losses. There is therefore a need for developing mitigation tools in order to reduce the occurrence and impact of skin lesion/ulcers, which require reproducible challenge models to do so. With the increased use of lumpsuckers as a biological sea lice control, issues have emerged regarding their welfare and the diseases that impact them. One particular problem is the risk of pathogen transference between these two species kept in cohabitation.

Tenacibaculum finnmarkense is the main causative agent of tenacibaculosis in Atlantic salmon smolts in Northern Norway. This bacterium has also been associated with the disease, “crater disease” in lumpsuckers. Previous fish experiments have shown that the disease can be replicated in laboratory conditions with certain strains of T. finnmarkense using a bath infection model and salmon smolts. A challenge model has not been developed for lumpsuckers.

Tenacibaculum maritimum is a fish pathogenic bacterium that causes significant losses in a wide variety of aquaculture fish species (including Atlantic salmon) worldwide. It was first identified in Norwegian aquaculture in 2015 in association with increased mortality in farmed lumpsuckers. T. maritimum has since been found in gills from farmed Atlantic salmon with poor gill health. The strains isolated from these lumpsuckers and Atlantic salmon are closely related to strain of T. maritimum that cause significant disease in Atlantic salmon in British Columbia, Canada. Experiments have shown that T. maritimum is easily transmitted from fish to fish and there could therefore be a risk if transferring T. maritimum infected lumpsuckers into Atlantic salmon pens or vice versa.

This experiment will develop/refine challenge models for Norwegian strains of T. finnmarkense and T. maritimum in both Atlantic salmon smolts and lumpsuckers. This will be used to develop management tools to reduce the impacts of these pathogens in the Norwegian aquaculture industry, including vaccines and better husbandry practices. The potential horizontal transfer of T. finnmarkense and T. maritimum from lumpsuckers to salmon will also be investigated. A total of 590 Atlantic salmon and 290 lumpsuckers will be used in the study (total: 880 animals). Some fish will experience disease. To reduce their suffering and discomfort to a minimum strict surveillance of humane endpoints will be enforced. The objectives of the experiment cannot be carried out without the use of laboratory fish. The number of fish is reduced to a minimum for what is necessary to provide sufficient quality data.