Advantages of nighttime lighting for growth of juvenile Pacific bluefin tuna Thunnus orientalis

During the fingerling production process of Pacific bluefin tuna (PBF), Thunnus orientalis , heavy mortality can occur immediately after the transportation of juveniles from nursery tanks to sea cages and the nighttime lighting moderates this mortality. It has been confirmed that various wild live prey gathered under nighttime lighting in practical sea cage culture of PBF. We validated the effectiveness of nighttime lighting to combat mortality by examined its effects on PBF growth and survival. To prove this, the present study was performed in land-based tanks, such that changes in environmental conditions did not affect the experiment. We investigated whether the growth and viability of PBF juveniles could be improved by promoting feeding live preys under nighttime lighting (treatment; Nigh-Feed, n = 4) and compared them with negative control group which were not fed during night (Control, n = 4). Results showed that growth was significantly improved under the Night-Feed group in which 69–78% of juveniles showed evidence of having fed during the night. However, the rate of survival was statistically similar between the group. It is anticipated that nighttime lighting plays an important role to gather various live preys during night and PBF juveniles consumed these feed items in sea cage. This could partially serve as a countermeasure against heavy mortality occurs in sea cage by promoting juvenile growth.