Juvenile Pacific oysters Crassostrea gigas were fed the toxic dinoflagellate Gymnodinium catenatum, a producer of paralyzing shellfish poisoning (PSP) toxins, and dinoflagellate Alexandrium margaleffi as non-toxic control. We investigated how G. catenatum influenced feeding rates, toxin accumulation-depuration, and transcriptomic response in C. gigas in the whole organism. Depletion of algal cells was measured in closed systems, and oysters fed toxic dinoflagellates have low feeding activity compared to oysters that provided non-toxic dinoflagellates.