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Abstract--Morphological development and growth of larval and juvenile Pacific bluefin tuna, Thunnus thynnus, were studied from laboratory-reared specimens. Average body length (BL) of newly hatched larvae was 2.83 mm and [...]

The effects of different aeration rates at night to prevent sinking syndrome-related death (SSRD) of the tiger grouper, Epinephelus fuscoguttatus were examined. The aeration rates were fixed at 300 mL min -1 at daytime (07:00-19:00 hours) and regulated to 0, 300 and 900 mL min -1 at night (19:00-07:00 hours). Larval survival, growth, feeding intake, sinking velocity, distribution and behaviour, stress level, surface tensionrelated death (STRD) and flow velocity distribution were assessed. The occurrence of SSRD in the tiger grouper was observed through the accelerated sinking velocity (Vl) (from 0.15 ± 0.09 cm s -1 at 4 days AH to 0.41 ± 0.09 cm s -1 at 12 days AH) coupled with larval passive swimming behaviour at night-time. On the final day of experiment (15 days AH), larvae reared in 900 mL min -1 at night had attained significantly higher (P < 0.05) survival (34.4 ± 5.5%), growth (5.8 ± 0.5 mm) and feeding intake (60.46 ± 6.98 ind. larva -1). A favourable flow field for the tiger grouper was produced in 900 mL min -1 at night-time, in which larvae were transported 15-25 cm above the tank bottom and 1.0 cm beneath the water surface. Under these night-time rearing conditions, larval stress level and number of STRD reared in 900 mL min -1 compared with those observed in 300 mL min -1 remained insignificant, indicating that strong turbulence of flow velocity was not detrimental for larvae. Our findings recommend aeration at 900 mL min -1 at night as this could improve larval survival by reducing SSRD. [ABSTRACT FROM AUTHOR]

This study examined the influence of swimbladder inflation ( SBI) failure on mortality (Experiment 1), lordotic deformity (Experiment 2) and growth (Experiment 1, 2) in Pacific bluefin tuna, Thunnus orientalis, postflexion larvae and juveniles by producing larvae lacking inflated swimbladders. Experiment 1 was conducted for postflexion larvae to juveniles (from 18 to 30 days-post-hatch; dph). Mortality was not significantly different between the fish with ( WIS) and without ( WOIS) inflated swimbladders. Standard length ( SL) and body weight ( BW) were significantly smaller in WOIS than WIS. Moreover, the SBI was found in WOIS after postflexion stage. In Experiment 2, two examination trials were conducted on SBI, vertebral deformity and growth for juvenile stage. Lordotic deformities were found neither in the WOIS nor in the WIS. Although SL and BW were significantly smaller in WOIS than WIS at 22 dph, after 37 dph no significant differences were found between them. The results of Experiment 1 and 2 indicate that SBI failure causes growth retardation until juveniles of 30 dph; however, it does not cause growth retardation in juveniles after 37 dph and mortality of postflexion larvae and juveniles. Moreover, SBI failure did not cause lordotic deformity in PBT differently from many other fish. [ABSTRACT FROM AUTHOR]

This study investigated the optimal timing of day to promote initial swimbladder inflation ( ISI) for improved Pacific bluefin tuna ( PBT), Thunnus orientalis, larval survival. Larval swimbladder inflation frequency was compared based on three experiments using different time schemes of surface film removal ( SFR) from 3 to 9 days post hatch (dph). SFR was conducted from 05:00 to 19:00 hours (light period: S.5-19), 19:00 to 05:00 hours (dark period: S.19-5), 08:00 to 19:00 hours (S.8-19) and the entire day (S.24) in Experiment 1; from 08:00 to 19:00 hours (S.8-19-E2), 08:00 to 13:00 hours (S.8-13), 13:00 to 19:00 hours (S.13-19) in Experiment 2; and from 13:00 to 16:00 hours (S.13-16), 16:00 to 19:00 hours (S.16-19), 18:00-19:00 hours (S.18-19) in Experiment 3. The swimbladder inflation frequency at the experiment termination (9 dph) was significantly higher ( P < 0.001) in S.24 (91.1 ± 5.7%), S.5-19 (92.2 ± 5.1%) and S.8-19 (93.3 ± 3.4%) than in S.19-5 (11.1 ± 5.1%) in Experiment 1, and remarkably higher in S.8-19-E2 (81.7%) and S.13-19 (88.3%) than in S.8-13 (0.0%) in Experiment 2, and significantly higher ( P < 0.001) in S.16-19 (84.4 ± 5.1%) and S.18-19 (70.0 ± 12.0%) than in S.13-16 (7.8 ± 3.9%) in Experiment 3. These results suggest that the optimal timing to promote larval ISI by SFR is a few hours before the end of light period (16:00-19:00 hours) from 3 to 9 dph. [ABSTRACT FROM AUTHOR]

Juvenile Pacific bluefin tuna ( Thunnus orientalis; PBT) often experience high mortality during ship transportation. This study investigated whether the addition of colours or patterns to the walls of tanks affected survival rate. In the first experiment, three colours and lattice patterns were tested: dark blue single-colour, red single-colour, and red-blue lattice pattern. Fish in all tanks exhibited abnormal behaviours when sunlight entered the tanks between 0800 and 1000 hours, but mortality only increased in the single-coloured tanks as a result of collision with the tank walls. In the second experiment, four colours and patterns were tested: dark blue single-colour, red-blue lattice pattern, red-blue lattice pattern with shade sheet and red-green lattice pattern with shade sheet. Again, we visually observed that fish in all treatment groups exhibited abnormal behaviour when sunlight entered the tanks, but there were no collision deaths in the lattice-patterned tanks and survival in this group was significantly higher than in the single-coloured tanks. Thus, the use of a high-contrast colour pattern can prevent mass death of juvenile PBT during ship transportation. [ABSTRACT FROM AUTHOR]

This study investigated the influence of initial swimbladder inflation ( ISI) failure on survival of Pacific bluefin tuna ( PBT), Thunnus orientalis, larvae to prevent mass mortality due to sinking death. In Experiment 1, swimbladder inflation frequency and survival within an ISI promoted ( PS) group, for which surface film of rearing water was removed, and a group without ISI promotion ( NPS) were compared in 20 and 30 kL tanks. The PS group demonstrated significantly higher swimbladder inflation frequency and increased survival than the NPS group within 20 kL tanks at 9 days post hatching (dph). Similar tendencies were observed within 30 kL tanks. In Experiment 2, larval distribution and swimbladder inflation frequency in the night-time were examined through larval sampling within the upper and middle layers of the water column and tank bottom within 1.6 and 30 kL tanks at 5 dph. Larvae at tank bottom had higher distributional density and significantly lower swimbladder inflation frequency than those distributed in the upper and middle layers within 1.6 kL tanks. Similar tendencies were observed within 30 kL tanks. Results of this study suggest the improvement of larval survival due to prevention of sinking death through ISI promotion in mass-scale PBT larviculture. [ABSTRACT FROM AUTHOR]

Flow field control via aeration adjustment for the enhancement of larval survival of the kelp grouper Epinephelus bruneus was examined. Aeration rate of 300 mL min−1 was introduced during daylight (07:00-19:00 hours) and adjusted to 0, 300 and 900 mL min−1 at night (19:00-07:00 hours). Larval sinking velocity±SD increased from 0.08 ± 0.05 to 0.26 ± 0.24 cm sec−1 from 4 to 12 days after hatching (DAH), indicating their susceptibility to sink. Larvae reared in 300 mLmin−1 attained the highest survival rate at 24.9 ± 3.4%, but remained significantly smaller in growth: 4.54 ± 0.56 mm compared with 4.82 ± 0.53 mm in 900 mL min−1. The flow field in 300 and 900 mL min−1 was at 10-20 and 15-25 cm above the bottom of the tank and 8.0 and 1.0 cm beneath the water surface. A favourable rearing condition was observed in 300 mL min−1 as larvae were away from the bottom and surface areas, thus preventing them from dying due to sinking and surface tension-related death (STRD). Although sinking death was decreased with an increasing aeration rate, the stronger flow had increased larval susceptibility to STRD. Our findings suggest that aeration at 300 mL min−1 could enhance larval survival by reducing both sinking death and STRD. [ABSTRACT FROM AUTHOR]