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

Abstract

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.

Enhancement of survival rate of Pacific bluefin tuna (Thunnus orientalis) larvae by aeration control in rearing tank

“…Kayaba (2003) reported that aeration reduced mortality in barfin flounder (Verasper moseri) larvae at early-stage settlement. Similarly, larval sinking and survival in seven-band grouper (Epinephelus septemfasciatus) is related to aerator distribution and air supply (Shiotani et al 2003), and to the pattern of circulation in the rearing tank (Sakakura et al 2006). Teruya et al (2009) quantified the flow field that prevented the sinking of amberjack larvae, and Tanaka et al (2009) demonstrated that the number of sinking PBT larvae was decreased by vertical turbulent mixing of the rearing water through aeration.…”

Relationship between Aspect Ratio and Flow Fields in a Rearing Tank

“…Comparing the very large tank employed by Sakakura et al to the cases in this study, the flow in the tank corresponds to the case shown in Fig. 4, in which a high survival rate for the larvae is not necessarily expected [5]- [6]. Therefore, in this case, a double vortex in the vertical direction, as for AR = 2.0, is not formed.…”

“…For example, the Nagasaki Prefectural Institute of Fisheries in Japan uses a cylindrical tank for fish rearing with a diameter of 8 m, a depth of 2 m, and a tank water capacity of 100 m 3 [5]- [6]. For this tank, the AR is 0.47.…”

Isolation and characterization of polymorphic microsatellite loci from a dinucleotide-enriched genomic library of seven-band grouper (Epinephelus septemfasciatus) and cross-species amplification

“…Like most other epinephline groupers, it exhibits protogynous hermaphrodite life history undergoing sex reversal from female to male. Due to the particular sex inversion characteristic and high economic value, many documents have focused on studying reproductive physiology, protective immunity, and broodstock management for seedling production (Nagano et al 2007;Tanaka et al 2001;Sakakura et al 2006). The resource of seven-band grouper is facing a high risk of becoming threatened in the near future if no conservation action is taken (Morris et al 2000).…”