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.