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Context and Objectives

The context of strong socio-economic and environmental constraints to world aquaculture production suggests the need to manage product quality to ensure its sustainability. Among quality parameters, flesh texture is essential, not only for sensorial properties of the product but also for its suitability for processing into filets. Texture is determined by the nature, quantity and properties of the components, mainly protein-based, of muscle, but also by the three-dimensional organisation (structure) of those tissues (muscle, connective and adipose) of which it is composed. Flesh texture is thus a complex phenotype that depends on relative developmental rates of different muscle tissues. The understanding of the biological basis of this texture implies having experimental models with given textural characteristics. Our preliminary work has shown that parameters of mechanical resistance of filets measured within hours after slaughter have moderate heritabilities (0.25-0.47), which suggest significant genetic determinism of these properties. To understand the development of the texture phenotype and its variability in more detail, it would be appropriate to perform divergent selection on this trait to obtain extreme genotypes that would furnish a relevant biological model. Nonetheless, this approach remains expensive and takes a long time to obtain sufficient divergence, especially since a trait such as texture cannot be measured directly in the candidates for selection.

Discussions with geneticists, in the framework of the strong collaboration of this project, have identified the relevance and originality of using the isogenic strains that they developed (E. Quillet, GABI). Each strain is composed of completely homozygous individuals, all of which are genetically identical. Until now, for all traits studied, a large phenotypic divergence between strains has been observed. This material has already been used successfully to study disease resistance or feed use (collaboration GABI-Numea). In addition, since the strains are stabilised, genotypes can be produced as often as necessary. The GABI unit is a full stakeholder in the project and contributes financially to the project by the production and maintenance of these isogenic strains. The parameters of flesh quality in this unique material have never been characterised before and thus would be a relevant alternative to divergent selection for furnishing extreme genotypes.

The objective of this project is to identify the genotypes corresponding to extreme textures that will be relevant biological models to understand in greater detail the development of the phenotype of flesh texture and its variability. Once the model is validated, higher-resolution phenotyping of muscular characteristics will be performed for fish in the extreme strains.