This study examined the effects of hydrodynamic conditions on the growth performance and nutritional quality of Pacific oysters (Crassostrea gigas) in raceway flumes. Oysters were reared under three flow velocities—low (LV, 5 cm/s), medium (MV, 10 cm/s), and high (HV, 20 cm/s)—using three replicate flumes per treatment, each containing 100 individuals. Results indicated that while shell morphology remained unaffected by flow rate, MV significantly enhanced soft tissue weight and meat yield compared to LV. Physiologically, HV upregulated the activities of trypsin and amylase, with trypsin levels significantly exceeding those in LV. Furthermore, MV exhibited the highest crude protein and glycogen content. Notably, both MV and HV improved the accumulation of total and essential amino acids. Fatty acid profiles showed clear separation among treatments, primarily driven by C16:0, C18:0, C20:5n3, C22:1n9, and C20:2. Collectively, moderate flow velocity (10 cm/s, MV) resulted in a well-balanced enhancement of growth, biochemical composition, and nutritional value compared to low or high velocities, highlighting the potential value of controlled hydrodynamic conditions in oyster farming.