Impact of Dietary Lipid to Carbohydrate Ratio on Elemental Stoichiometric Relationships in Growth Phenotypes of <i>Ruditapes Decussatus</i>

Understanding the mechanisms of nutrient regulation in bivalves is crucial for optimizing their growth under varying dietary conditions. In the present work, juveniles of the carpet shell clam (<i>Ruditapes decussatus</i>) from the same cohort were size-segregated to obtain fast and slow growing phenotypes. These clams were then conditioned to diets presenting a range of lipid/carbohydrate proportions but similar carbon:nitrogen (C:N) ratios. Subsequently, experiments were conducted to determine elemental (C and N) balances in order to achieve the following aims: (a) To identify strategies of homeostatic nutrient regulation in relation to either endogenous (growth phenotype) or dietary factors and (b) to quantify the extent to which stoichiometric adjustments (at both pre- and postabsorptive levels) are accomplished throughout the successive components of elemental balances. The elemental balances of both C and N exhibited higher values under the lipid-rich diets, indicating the presence of nutritional limitations in juvenile clams fed on low lipid/carbohydrate proportion, resulting from a greater digestive imbalance of lipids in diets of low digestibility coupled to limited dietary lipid income. These nutritional limitations were more effectively managed by the fast-growing phenotype, pointing to the importance of enhanced energetic status in sustaining homeostatic nutrient regulation. The stoichiometric coupling between consumed diets and the biosynthetic requirements of growing tissues relied on postabsorptive rather than preabsorptive mechanisms, although notable discrepancies in this regard were observed between conditioning diets.