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Optimal periods of night-time lighting in the sea cage culture of Pacific bluefin tuna, Thunnus orientalis, juvenile (Temminck and Schlegel)

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Abstract

We have previously reported that night-time lighting prevents the mass death of Pacific bluefin tuna (PBT) juvenile due to collision and/or contact with the walls of sea cages, immediately after transfer to the cages, and that night-time lighting does not negatively impact fish stress levels. However, the period of night-time lighting should be limited to minimize negative impacts on the surrounding environment and aid management. Therefore, we investigated the optimal period of night-time lighting by evaluating the whole-body cortisol and glucose levels as stress parameters, growth performance and survival of PBT juvenile in four cages with different periods of night-time lighting (i.e. unlit, 4-day, 8-day and 12-day lighting). The results showed that almost all fish were died 1 day after transfer to the unlit cage. In comparison, the other groups (4-day, 8-day and 12-day lighting) had high survival rates (92.5–96.0%) without significant difference. However, in the 4-day-lighting group, an obvious stress response was recorded on day 5, and growth performance was significantly lower. In the 8-day-lighting group, whole-body cortisol levels were slightly elevated on day 9; however, significantly elevation was not recorded on day 12. These results indicate that the recommended lighting period of night-time lighting in sea cages is 8–12 days.

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