A flow in a cylinder tank is the flow that even fisheries engineering is seen in as well as chemical engineering. The object of this study is the flow in a rearing tank with regard to fisheries engineering. Recently, the cultivation of high efficiency has been required as well as fishery to save resources in fishery. Marine fish larvae are fragile against physical stress. However, few studies have been conducted to evaluate the flow field in a rearing tank, which is assumed to provide a high degree of physical stress to marine fish larvae. Therefore, I attempt to quantify and visualize the flow field by aeration in the rearing tank with hydrodynamics approach. The first step is flow visualization. Flow visualization has carried out to grasp flow pattern in rearing tank. When the ratio depth to diameter H/D exceeded 0.59,flow pattern in rearing tank was ransrated, regardless of aerating rate.