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Objectives

The control of pathogens in fish farming is a major goal for its sustainability. Commercial vaccines are few in number and often not very effective. The use of sanitizing agents and antibiotics is often the only recourse, but they pose problems for food safety and/or emissions to the environment. Selection of resistant strains is the most promising alternative. The objective of the project underway is thus to better understand the immune mechanisms involved in trout, and in fish in general, and identify the genetic basis of resistance/sensitivity (heritability, quantitative trait loci (QTL) and the genes responsible) so as to effectively introduce disease resistance in commercial selection programs.

The work is performed mainly on a virus, viral haemorrhagic septicaemia (VHS), and a bacterium, Flavobacterium psychrophilum, the cause of bacterial cold water disease (BCWD).

Experimental Framework

Experimental strains are maintained at PEIMA, mainly representing a collection of isogenetic lines obtained by gynogenesis. These strains have been systematically challenged with different viruses (VHS, infectious hematopoietic necrosis (IHN), infectious salmon anaemia virus (ISAV)) and bacteria
(F. psychrophilum or Aeromonas salmonicida). High variability in sensitivity has been observed among lines, regardless of the pathogen. The strains with extreme resistance are then used, either directly to study differences in response of the gene pools or to produce recombinant strains (F1 and F2 crosses, retrocrosses, advanced crosses) used to map QTLs.

Standard family approaches (factorial crosses with the reference strain SY) are also set up to assess classic genetic parameters (heritability, genetic correlations between traits).

The experimental crosses are performed at PEIMA. At the end of incubation, eggs are transported to IERP, which performs experimental infection trials under controlled conditions. Strict health management of breeders is essential to ensure the production of immunologically “naïve” fish.

Research Unit Partners

• INRA : Molecular Virology and Immunology research unit, Animal Health department
• INRA : Rodent and Fish Experimental Infectiology experimental unit (IERP, Jouy-en-Josas), Animal Health department