Promotion of initial swimbladder inflation in Pacific bluefin tuna,Thunnus orientalis (Temminck and Schlegel), larvae

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, and SF6D (17.8–7.5%). 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.