The EU project "GENEPHYS", initiated by the IFREMER laboratory GAP-La Tremblade (Génétique Aquaculture et Pathologie) and CREMA-l'Houmeau (Centre de Recherche en Ecologie Marine et Aquaculture), aims to establish the relationships between physiological traits involved in growth (oxygen consumption, absorption efficiency, scope for growth) and their genetic bases (determinism, variability within and among populations) in cupped oyster Crassostrea gigas. The main bjectives are : 1. To express the maximum variability of growth, both at the larval stage and at the adult stage, in a oyster population originating from parents of various origins. 2. To check the persistence over the time, of growth performance and related physiological functions. 3. To explain the observed growth differential by physiological functions studied. 4. To establish whether, using 2 types of markers (allozymes and microsatellites), the growth differential of physiological functions is associated with a genetic basis, and whether this is related to aneuploidy and the identity of missing chromosomes. 5. To estimate, in a second generation, genetic variance (additivity, dominance) and heritability of growth and of related physiological traits. Also to estimate aneuploidy transmission to this generation. 6. To evaluate the possibility of selection for a better assimilation efficiency. The beginning of a genetic map provides the first step for marker- assisted selection and QTL (Quantitative Trait Loci) location.