Marine fish larvae are fragile against physical stress. However, few studies have been conducted to evaluate the flow field in rearing tanks. The flow field is generated by aerators, which are commonly used to provide oxygen as well as aid in the even distribution of live food. The procedure of fluid dynamics was used to analyze the flow field in rearing tank (1m³ polyethylene tank) of seven band grouper larvae. Among fish species, grouper larvae are highly sensitive to physical stress ; mass mortality caused by flotation has been commonly reported. When aerating rate exceeded 500ml/min, strong vertical circulating flow was observed, and production of air bubbles at faster rate will have increased the chance of direct physical damage to larvae. The fast water flow can also have caused a decrease in encounter rate between larvae and prey organisms. When aerating rate was below 200ml/min, there was no water movement in the central body of the vertical circulation flow. This area probably did not receive direct supply of oxygen from the aerator, which may have affected physiological status of larvae distributed in the area. The estimation based on fluid dynamics analysis was consistent with experimental data of larval growth, feeding incidence, and mortality obtained from larval rearing trials. Aerating rate at 200ml/min gave highest survival and growth of grouper larvae.