The diet of juveniles in rivers and brackish waters is essentially composed of benthic macroinvertebrates but their exact identification is difficult given the rapid degradation of the bolus.  In the Gironde estuary, the analysis of stomach contents has shown that polychaeta worms and small crustacean species are the main source of food for young sturgeons (Brosse et al, 2000 a & b).
The main taxa consumed have been identified as:

- Polchaeta worms (Heteromastus sp., Nereis sp., Polydora sp.). - Small Crustaceans          - Amphipods: Bathyporeïa sp., Corophium sp., Gammarus sp. ;         - Isopods: Cyathura sp., Syntidotea sp. ;         - Decapods: Carcinus sp., Crangon sp. ;         - Mysidacae - Fish (Pomatoschistus minutus).

Spatio-temporal preferences shown by the juveniles for certain areas of the Gironde estuary are likely to be influenced by seasonal fluctuations in the abundance of food. Periodic, but optional, migration of young sturgeon outside the estuary would also meet these needs.  Scientists suspect that there are zones of sturgeon concentration or rearing zones at sea, close to the mouth of the estuary.