Improvement of the survival in the seven‐band grouper Epinephelus septemfasciatus larvae by optimizing aeration and water inlet in the mass‐scale rearing tank

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