Effect of a long photoperiod on the timing of spawning in the Pacific bluefin tuna, Thunnus orientalis

In this study, we examined the effects of a long photoperiod on the reproduction of Pacific bluefin tuna (Thunnus orientalis) in a land-based tank. Three-year-old fish were shifted from a short (10.5 L:13.5D) to long (15 L:9D) photoperiod in December. The broodstocks exhibited gonadal development after this photoperiod change and spawned spontaneously the following March, approximately three months earlier than the normal spawning season. Although the results were based on data from a small sample size of fish, the study suggests that a long photoperiod induces the onset of gonadal development in Pacific bluefin tuna, thereby accelerating their spawning time.