Abstract: This study provides a comprehensive analysis of the embryonic and early larval development of Platypharodon extremus, an endemic and endangered fish species inhabiting the upper Yellow River basin. Our experimental results demonstrate that fertilized eggs exhibit pale white coloration, demersal characteristics, and slight adhesiveness, with mature eggs measuring (1.71±0.11) mm in diameter that expand significantly to (2.78±0.10) mm after water absorption. Under controlled temperature conditions (13.1±0.58) °C, the embryonic developmental process required precisely 207 hours and 59 minutes to complete hatching, corresponding to a cumulative thermal unit of 2 687.58 h·℃. Notably, the embryonic development of Platypharodon extremus displays three distinctive sequential patterns: (1) otic vesicle formation preceded tail bud emergence; (2) lens crystallization occurred prior to muscle contraction; (3) otolith appearance followed heartbeat initiation. Newly hatched larvae measured (6.60±0.21) mm in total length, demonstrating rapid developmental progression. Critical milestones included: (1) achievement of swim bladder inflation and horizontal swimming capabilities within 7 days post-hatching (d); (2) complete absorption of yolk reserves by 12 d; (3) successful transition to exogenous feeding at 12 d. These accelerated developmental traits are interpreted as adaptive evolutionary responses to the dual challenges of low water temperatures and limited food availability characteristic of the upper Yellow River's alpine environment. The significance of this research extends beyond fundamental biological knowledge. By establishing the first detailed developmental timeline for this endangered species, the study fills critical gaps in our understanding of cold-adapted fish developmental strategies. These findings have direct implications for conservation efforts, particularly in informing: (1) the design of artificial propagation protocols; (2) habitat restoration initiatives for hydropower-affected river sections; (3) the implementation of species-specific protection measures in the context of climate change. The dataset generated provides essential baseline information for future studies on the evolutionary ecology of high-altitude fish species and contributes to the scientific foundation for sustainable management of the upper Yellow River's aquatic biodiversity.