Effects of photoperiod on survival, growth and feeding of Pacific bluefin tuna Thunnus orientalis larvae
2018
Kumon, K. ((Nagasaki University, Nagasaki (Japan). Graduate School of Fisheries and Environmental Sciences), (Seikai National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Oshima, Kagoshima (Japan). Research Center for Tuna Aquaculture, Amami Laboratory)) | Tanaka, Y. | Ishimaru, C. | Sakakura, Y. | Eba, T. | Higuchi, K. | Nishi, A. | Nikaido, H. | Shiozawa, S. | Hagiwara, A.
One of the major problems in the larviculture of Pacific bluefin tuna (PBT) Thunnus orientalis is sinking syndrome; larvae die by sinking to the bottom of rearing tanks during nighttime. We evaluated the effects of different photoperiods on survival, growth and feeding of PBT larvae in small tanks and mass-culture tanks. First, larvae were reared until 8 days after hatching in 500 l tanks under 2 different photoperiods; 14L : 10D and 24L : 0D (2,000 lux). Larval survival was 9-times higher under 24L : 0D (15.5 ± 7.6%) than 14L : 10D (1.8 ± 0.6%). Larvae at 24L : 0D was significantly larger than those at 14L : 10D. The number of larval gut content was the highest before light-out in 14L : 10D group and was few during dark period. Larvae in 24L : 0D continuously fed on rotifers, while the lowest larval gut contents was observed at 3 a.m. Secondly, we reared PBT larvae until 10 days after hatching in 2 rearing tanks (40 kl) under 2 different photoperiods; 24L : 0D and 14L : 10D. Survival of larvae under 24L : 0D (29.3%) was about 10-times higher than 14L : 10D (3.1%), while there was no significant difference in growth between treatments. These results indicate that 24L : 0D condition improved survival of PBT larvae.
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