Energetic scaling mechanisms underlying family growth variation in Ruditapes decussatus

The grooved carpet shell (Ruditapes decussatus) is a commercially valuable bivalve species facing declining production due to limited natural recruitment and high inter-individual variability in growth. This study aimed to identify the growth variation at both inter-family and intra-family levels over short- and long-term periods. Four full-sibling families (i.e., offspring from one female × one male) were produced and reared under identical hatchery conditions. Individuals covering the full range of growth rate variation were sampled during the juvenile and adult stages (experiments initiated at 4 and 18 months post-fertilization) to assess physiological parameters related to energy acquisition and metabolism. Intra-family differences in growth were more pronounced than inter-family differences, with full siblings displaying over two orders of magnitude in live weight after only 4 months, a pattern that persisted over time. Allometric analysis revealed that faster-growing individuals displayed equal or higher feeding and routine metabolic activity per unit mass compared to their slower-growing siblings, after accounting for differences in body size. These results suggest that intrinsic differences in filtering capacity are the main physiological contributor of intra-family variation in growth performance. Limited but significant inter-family differences were also observed in physiological scaling parameters, supporting the role of genetic background in influencing growth. Overall, our findings highlight endogenous filtering capacity as the primary physiological mechanism underlying growth variability in R. decussatus, providing mechanistic insight into energetic regulation of growth in marine bivalves.