Plant protein blends in diets for Senegalese sole affect skeletal muscle growth, flesh texture and the expression of related genes

Abstract Skeletal muscle growth and flesh quality were evaluated in Senegalese sole fed plant protein (PP) diets. A control fish meal-based diet (FM) was compared with three isonitrogenous (54%) and isolipidic (9%) diets with increasing levels of PP blends (50% PP50, 75% PP75 and 100% PP100). By the end of the experiment sole fed PP50 and PP75 had a body length similar to the CTR (25 cm), but fish fed PP100 were significantly smaller (23 cm). Total FM replacement (PP100) resulted in significantly smaller muscle cross sectional area mainly due to a decrease in the muscle fibre size as the total number of fibres did not vary significantly among treatments. The dietary incorporation of PP significantly reduced the expression of several key genes involved in myogenesis and muscle growth (mrf4, fgf6, myhc and mylc2). Fillet texture was affected by the total substitution of FM. Fish fed PP100 diet had a significantly higher modulus of elasticity (lower flesh stiffness) compared with the other groups. Muscle fibre size was moderately related (r = 0.573) to the modulus of elasticity and positively correlated with the expression of lysyl oxidase (r = 0.495). Muscle cellularity changes were not associated with the expression of texture-related genes (capn2, ctsb, ctsd), since no significant differences were observed among diets. The present results point towards a modulation of the expression of several muscle growth related genes by increasing levels of PP sources that alter muscle cellularity and textural properties of Senegalese sole when total FM is replaced by PP. Statement of relevance The biological basis through which sustainable and practical plant protein diets (PP) affect flesh texture determinants is extremely scarce so the present results will be valuable to the aquafeed industry, fish producers and final consumers. This study clearly shows that PP diets reduced expression of several key genes involved in myogenesis and muscle growth and can hence affect fish growth potential at long term. This study identifies useful markers that correlated well with muscle cellularity and muscle growth and can be further used to select the most appropriate diets for a fish species.