To select the best microalgae for Ostrea edulis conditioning, four single species diets were fed to batches of broodstock, which were then compared using physiological and biochemical approaches. Ingestion and absorption were first studied, showing that Chaetoceros gracilis and Skeletonema marinoï were efficiently ingested (4.9–5.3 mg g−1 h−1) and absorbed (1.9–2.5 mg g−1 h−1) while Tetraselmis suecica led to the lowest physiological responses (0.36 and 0.12 mg g−1 h−1 respectively). When O. edulis were fed any microalgae except T-ISO with only 79 mg g−1, gonads accumulated carbohydrates from 116 to 141 mg g−1 and the extent of accumulation depended on the species supplied in the order T. suecica