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

International audienceFour microalgae species (Rhodomonas salina, Thalassiosira weissflogii, Thalassiosira pseudonana and Pavlova lutheri) were evaluated to estimate their potential as food for Ostrea edulis (L.) reproductive conditioning. Best ingestion and absorption were observed with R. salina (3.44 and 1.59 mg g− 1 h− 1, respectively), followed by T. pseudonana (2.75 and 0.98 mg g− 1 h− 1) and P. lutheri (2.40 and 0.91 mg g− 1 h− 1). Oysters fed T. weissflogii exhibited the lowest ingestion and absorption values (1.40 and 0.68 mg g− 1 h− 1). Proximate composition (proteins and carbohydrates) and lipid content (fatty acids and sterols) analysed in four main tissues (gonad, digestive gland, muscle and gills) also differed significantly with diet. Protein ranged from 355 mg g− 1 in the gonad of oysters fed P. lutheri to 837 mg g− 1 in gills of oysters fed T. weissflogii; whereas carbohydrates ranged from 17.5 mg g− 1 in gills of oysters fed P. lutheri to 271 mg g− 1 in gonads of oysters fed R. salina. An overall poor enrichment in total PUFAs across all diets masked some of their potential impact on nutrition. In gonad, however, the major polyunsaturated fatty acids (polar lipid fraction) were EPA (≈ 19% for oysters fed T. weissflogii and 14% for those fed P. lutheri) and DHA (17% for oysters fed P. lutheri and 15% for those fed R. salina). Sterol contents showed a clear transfer from food to oyster tissues except with P. lutheri, from which neither methylpavlovol nor ethylpavlovol (characteristic of Pavlophyceae) were detected in oyster tissues. Histological analysis showed that gametogenesis was active in oysters fed R. salina and T. weissflogii, whereas only low gonadic development occurred in unfed oysters or those fed P. lutheri. R. salina is accordingly highly recommended for O. edulis broodstock conditioning whereas P. lutheri should be excluded

Survival, growth and fatty acid composition of Ostrea edulis larvae (L.) fed four different single species, microalgal diets, Tisochrysis lutea (T), Chaetoceros neogracile (Cg), Skeletonema marinoi (Sm) or Tetraselmis suecica (Ts) from broodstock to pre‐settlement, were studied. Lower larval growth (5.5 μm to 6.5 μm/d) was recorded in progeny continuously fed single S. marinoi or T. suecica, whereas good growth was achieved with single T. lutea (7.8 μm/d). Larvae, originated from broodstock receiving Sm or Ts, exhibited growth compensation when fed a bispecific balanced diet (TCg). This did not occur when broodstock and larvae were fed Cg or T, for which single or mixed diets led to similar larval growth. Furthermore, survival was high (>90%) regardless of microalgal diet, except for larvae fed from broodstock to pre‐settlement T (53%) or Ts (2%). There were significant differences in 20:5 (n‐3) and 22: 6 (n‐3) contents in polar and neutral fractions of O. edulis expelled larvae dependent on broodstock diet, as well as throughout larval development, but no clear trend was apparent when comparing fatty acid (FA) relative composition of both fractions of O. edulis larvae fed different diets at release or prior to settlement. In contrast, such correlation occurred when FA was expressed in absolute content but exclusively for larvae‐fed single diets and was particularly noticeable between 22: 6 (n‐3) and growth and survival. In the present work, broodstock nutritional deficiencies have been revealed in O. edulis progeny, compensated thereafter by feeding the larvae a mixed diet, and in this balanced condition, no obvious relation with larval development indicators was found with main fatty acid contents.