Abstract: The early-stage larval development of Penaeus monodon involves continuous dietary shifts, and the compatibility of feed type, feeding timing and prey density directly affects hatchery survival and larval quality. Current intensive hatchery practice still lacks feeding protocols based on these transition patterns. This study tracked the dietary transition of early-stage P. monodon larvae by microscopic observation combined with fluorescent tracing. To evaluate diet effects at the first zoeal stage (Z1), different microalgal species and feeding densities were compared for their effects on larval survival and metamorphosis; the point of no return (PNR) was determined in separate starvation trials. At each developmental stage, amylase, protease and lipase activities were assayed and the amylase-to-protease ratio (A/P) calculated, so that changes in digestive enzyme activity could be linked to the dietary shift. Results showed that P. monodon shifted from endogenous nutrition to herbivory at Z1 and from herbivory to carnivory at Z2. At the first postlarval stage (P1), larvae actively switched to preying on Artemia nauplii. Thalassiosira sp. and Chaetoceros sp. were the optimal microalgal diets for Z1 larvae, both best fed at 5×10⁴ cells·mL⁻¹. Values were means±SD. Survival and metamorphosis in Thalassiosira group reached (100.0±0.00)% and (96.67±1.15)%, versus (98.67±1.15)% and (92.56±2.40)% in Chaetoceros group. Z1 was also the critical window for building exogenous nutrient reserves, since the PNR occurred about 16 h after starvation began. Rotifer grazing followed the Holling type II functional response. The absolute feeding rate saturated near 30 ind.·mL⁻¹ from Z2 to M3; at this prey density, stage-specific intake from Z2 to P1 was (21.4±3.8), (22.8±3.4), (25.8±2.2), (31.9±3.9), (33.6±1.7) and (16.9±3.7) ind., respectively. The A/P ratio fluctuated with development in close agreement with the dietary shifts and could serve as a physiological indicator of dietary transition. These findings provide practical guidance for optimizing feeding strategies and improving larval survival in shrimp hatcheries.