Initial swimbladder inflation (ISI) of Pacific bluefin tuna (PBT), Thunnus orientalis, larvae was studied to increase the survival of cultured larvae. Experiment 1 was conducted to explore promotion and inhibition of ISI under different water surface conditions; including the use of surface skimmer to remove autogenous surface substances (SS), covering the water surface with liquid-paraffin-layer (LP) and oil film (OF), and a control (non-treatment, NT). Significantly higher inflation frequency was observed in SS (62.2%) than NT (11.9%), LP (2.7%) and OF (3.9%). This indicates that ISI in PBT larvae can be promoted by removal of surface substances on rearing water which inhibit larval air gulping. Experiment 2 aimed to elucidate proper day of larval age to start skimming for promoting ISI with four different periods of oil film removal: from 3 to 8 (SF3D), 4 to 8 (SF4D), 5 to 8 (SF5D), 6 to 8 (SF6D) days-post-hatch (dph). Significant improvement in ISI frequency was observed in SF3D (80.2%) but the frequency was very poor in SF4D, SF5D,). This implies the need of oil film removal without missing a narrow window, 1 day of 3 dph, to promote ISI in practical PBT larviculture. Promotion of initial swimbladder inflation in Pacific bluefin tuna M. Kurata et al.

-High levels of larval mortality are a significant barrier to the artificial mass production of Pacific bluefin tuna (Thunnus orientalis). Mortality may occur when larvae sink and come into contact with the bottom of the rearing tank during the first 10 days after hatching. We evaluated the effect of flow control by aeration on the survival of T. orientalis larvae. These larvae were held in 500-L tanks in which the aeration rate was varied during the night. Larval survival increased with air supply. We documented the cross-sectional flow pattern and gravitational sinking velocities of larvae to assess the correlation between survival and circulation patterns in the tank. The sinking velocity of T. orientalis larvae at night increased with larval body density, which varied with swimbladder volume. Larvae with uninflated swimbladders sank significantly faster than larvae with inflated swimbladders. Both water circulation speed and survival increased at higher aeration rates. Our results suggest that aeration rates >900 ml min -1 may increase larval survival by counteracting sinking.

The e¡ects of delayed ¢rst feeding on the survival and growth of tiger grouper, Epinephelus fuscoguttatus (ForsskÔl 1775), larvae were examined under controlled conditions. The total length, yolk sac volume, oil globule volume, yolk sac absorption time and nutritional transition period (NTP) of the larvae fed at di¡erent ¢rst times (0, 6, 12, 18 and 24 h after the mouth opening stage; h AMO) were compared. Larval ¢rst feed intake was observed at 54 h after hatching (h AH) at 27.5 AE 0.5 1C. The yolk sac was consumed more rapidly with an increase in delayed ¢rst feeding and was signi¢cantly di¡erent among treatments (Po0.05). Larvae ¢rst fed at 0 h AMO had the longest yolk sac absorption (72 h AH) and NTP (20 h) times and had the highest survival and growth rates at the end of the experimental period (360 h AH), being signi¢cantly higher (Po0.05) than the other treatments. First mortality was observed at 69 h AH, approximately 2 h after point of no return (PNR) occurred. This study suggests that ¢rst feeding of tiger grouper larvae should commence at 0 h AMO for enhancement of larval survival and growth.

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