Fish flesh texture is a quality of importance both for consumer satisfaction and processability of fillets. Identification of biomarkers of texture is therefore of interest to predict fillet texture avoiding a destructive evaluation. Differentially expressed genes between "soft" and "firm" rainbow trout fillet were identified by a microarray approach, and their quantification by qPCR was developed. The level of expression of six genes coding for extracellular matrix protein was first successfully quantified and correlated to fillet firmness. Their expression was then quantified in three other experimental conditions known to produce different flesh texture. None of these genes were systematically related to fillet firmness in these experiments. The expression of only four genes (Cilp, Col5a1, Col1a3, Postn) were consistently related to fillet firmness when comparing marine- versus plant-based diet fed fish or fish from three isogenic lines. These results highlighted the complex and multi-molecular determinism of fish flesh firmness.