Influence of initial swimbladder inflation failure on survival of Pacific bluefin tuna, Thunnus orientalis ( Temminck and Schlegel), larvae.

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]