Status of the sinking of hatchery-reared larval Pacific bluefin tuna [Thunnus orientalis] on the bottom of the mass culture tank with different aeration design
2009
Tanaka, Y., National Center for Stock Enhancement, Setouchi, Kagoshima (Japan). Amami Station | Kumon, K. | Nishi, A,. | Eba, T. | Nikaido, H. | Shiozawa, S.
Underwater observations were conducted in order to investigate the status of the sinking of larval Pacific bluefin tuna in mass culture tanks (bottom area 19 square m, volume 50 cubic m) with two different types of water current made by weak (daytime) and strong (nighttime) aeration (Tank 1) and weak aeration during day and nighttime (Tank 2), which was used to reduce the number of the larvae sinking to the tank bottom. The number of sinking larvae on the bottom of the tanks was counted by the quadrat method (0.01 square m) from 2 to 8 days after hatching (DAH) at 23:00. In the Tank 1, the average density of the sinking larvae (individual/0.01 square m, n=9) was low (2.44/0.01 square m) during the observation period. In the Tank 2, the average density of the sinking larvae was significantly higher than in the Tank 1 and peaked on 5 DAH (15.6/0.01 square m). Although the difference in the survival rates between two tanks was not clear, our result suggests that the vertical mixing of the rearing water by aeration decreased the number of sinking larvae.
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