Effect on larval survival and growth by addition of polyethylene glycol and night-time lighting in Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel)
2019
Yamada, T. | Nakatsuka, N. | Hamasaki, M. | Kadomura, K. | Yoshikawa, S. | Matsumura, Y.
Low survival of early-stage larvae is a serious barrier for mass seed production of Pacific bluefin tuna (PBT) Thunnus orientalis. We conducted two experiments with the aim to improve the survival of early-stage PBT larvae, i.e. until 10 days after hatching (10DAH). In the first experiment, we tested the effects of addition of polyethylene glycol 6000 (PEG) (at 0 μg/ml, 1 μg/ml, 10 μg/ml) into the rearing tanks on PBT larval survival and growth (total length). The addition of PEG at 10 μg/ml tended to improve the survival rate at 10DAH, while addition of PEG at 1 μg/ml had no effect on larval survival. There were no differences in the total length at 10DAH between the three treatment groups. In the second experiment, we compared the effects of two methods, "night-time lighting" i.e. the new method and "night-time strong aeration'' which is currently the main method used, on prevention of early larval sinking death which leads to mass mortality of early-stage PBT larvae. The larval survival rate at 10DAH was not different between the two methods, "night-time lighting" and ''night-time strong aeration". But, the total length of PBT larvae at 10DAH with night-time lighting was significantly larger than that with night-time strong aeration. These results suggest that the addition of a high-dose PEG into rearing tanks and night-time lighting during the first 10 days after hatching are effective methods for improvement of survival or growth of early larval PBT.
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