Abstract: Background: The Manila clam (Ruditapes philippinarum), one of the most economically significant maricultured bivalves in China, faces critical challenges in genetic improvement due to the scarcity of high-quality breeding stocks. Triploid induction, a proven strategy for enhancing growth and survival in aquatic species, has yet to be systematically optimized for this species. While conventional methods have been applied in bivalve polyploidy induction, their efficiency and safety remain suboptimal. Approaches: To determine the optimal conditions for triploid induction in R. philippinarum using a hypotonic method, an orthogonal experimental design was employed to evaluate the effects of salinity (6, 8, 10, 12, 14, 16), induction timing (initiation of the first polar body extrusion, the time when 50% of the first polar body are extruded, and initiation of the second polar body extrusion), and induction duration (10, 15, 20 min) under controlled conditions (water temperature: (25 ± 0.5)°C; pH: 8.3 ± 0.1). Developmental metrics, including malformation rate, hatching rate, and triploid induction rate of D larvae, were quantified. The treated larvae were cultivated in filtered seawater for one month and the survival rates were assessed across different experimental groups. Results: The results demonstrated that the optimal induction protocol involved treating fertilized eggs with low-salinity seawater (salinity = 16) for 15 min after 50% of the fertilized eggs had extruded the first polar body. Malformation rate, hatching rate, and triploid induction efficiency were significantly influenced by salinity. Notably, the survival rates of larvae at early stages in the control group were significantly higher than those in the induced groups. Conclusion: This study showed that the hypotonic method enabled efficient triploid induction in R. philippinarum through combinatorially regulating salinity, induction duration, and critical developmental timing. The chemical inducers-associated toxicity could therefore be avoided and the triploid induction cost could be reduced. This study for the first time reported the triploid R. philippinarum production via hypotonic induction, laying a foundation for improving artificial triploid induction technologies in bivalve aquaculture.