Abstract
The high mortality rates of Pacific bluefin tuna (PBF; Thunnus orientalis) juveniles due to collision death can be alleviated by night-time lighting both in land-based tanks and sea cages; however, the optimal night-time lighting intensity and area of illumination for sea cages have not been systematically investigated. We addressed these issues in the present study using seven different night-time light intensities ranging from 0 as a negative control (NC) to 329.4 μmol m−2 s−1 covering the same area (Experiment 1) and different areas of illumination (0.12%, 1.34%, and 1.78% per cage; Experiment 2). The results of Experiment 1 showed that surface night-light intensity and survival rate were strongly correlated (r = 0.9643, P < .01), and significant differences were found among the three treatment groups, with survival increasing in the rank order of NC–1.2 < 4.5–38.0 < 116.7–329.4 μmol m−2 s−1 (Kaplan-Meier log-rank test, P < .001). The results of Experiment 2 showed no differences in survival when the area of illuminations was altered. There were no differences in growth performances in Experiments 1 and 2. These results indicate that providing night-time light intensity >116.7 μmol m−2 s−1 at the water surface can enhance PBF juvenile survival, and that light intensity rather than area of illumination is an important parameter in PBF sea cage culture.
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