Abstract: In order to determine the optimal size of aerating oxygen bubbles in recirculating aquaculture system, a single oxygen buble was investigated numerically during its rising from bottom to water surface. The investigation was analyzed by using fluid dynamic, thermal dynamic and physical-chemical principles and equations. According to the data of numerical calculation, the variations of the bubble in motion, size, and disslution were analyzed. Through optimization, relation curves between water depth and bubble size were obtained for different conditions.