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The water flow in larval rearing tanks has been indicated to cause mass mortality of the seven-band grouper (Epinephelus septemfasciatus) larva. Therefore, we tested a new aerating method in an actual scale of intensive rearing tank (8.0 m in diameter, 1.87 m 5 of water depth, 100 m 3 of volume), in which an aerator was set at the center of the rearing tank surrounding cylindrical drain (1.2 m in diameter) to generate the flow filed, and 7 larval rearing trials were performed. Then, we compared the survival rate with the former aeration methods, in which several aerators are located in the rearing tank. The survival rate at 10 days after hatching in the new aeration method (61.5 ± 5.1 %, n=7) 10 was about 3 times higher than the former methods (21.2 ± 13.7 %, n=6). We also examined the flow environment of rearing tanks by quantifying the flow field and discussed the relationship between the flow field in the rearing tank, behavior of larvae and survival. We confirmed that the vertical circulating flow was observed in rearing tanks, and determined effectively the survival and the behavior of grouper larvae in 15 patchiness.

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