Animals often face food scarcity in nature. In order to survive, some animals store substantial fat when food is available. However, the physiological mechanism by which they store substantial fat and maintain metabolic health in the short term is poorly understood. Here, using the grass carp (Ctenopharyngodon idellus) as a model, which exhibits remarkable fat storage capacity, we found that adipose tissue responded to energy overload first and expanded through adipocyte hypertrophy and hyperplasia.