Crassostrea virginica is an economically important oyster species that extends from the Gulf of Mexico to the Gulf of St. Lawrence where it experiences negative temperatures for 3-4 months in winter. In response to these low temperatures, adult oysters decrease the unsaturation index of their polar lipids during the fall to adjust the fluidity of their cell membranes and progressively reduce their metabolism to a near standstill in winter. During this dormant phase, oysters stop feeding and mobilizes their energy reserves to maintain their vital physiological functions. However, the metabolic strategies of oyster spats are still little studied, although they represent a crucial stage determining the production of adults and the economic performance of hatcheries. To better understand the energetic physiology of oyster seeds, we conducted two experiments from September 2021 to May 2022 and from September 2022 to May 2023 to follow the seasonal lipid dynamics and energy reserves of Crassostrea virginica seeds from fall acclimation to the end of winter dormancy. During this period, we analyzed the energy reserves and fatty acid composition of polar lipids of three size classes of juveniles from hatchery and wild origins. The results revealed homeostatic adaptation mechanisms in autumn, characterized by a gradual increase in polyunsaturated fatty acids within cell membranes in response to declining environmental temperatures (Figure 1). However, this lipid remodeling is reversed below a threshold of 2°C, marked by a sharp reduction in polyunsaturated fatty acid levels, potentially indicating the onset of spat dormancy (Figure 1). This dormancy, implying a halt in acclimatization to colder winter conditions, may partly explain the high mortality rates observed among juvenile oysters along the St. Lawrence coast.