Ontogeny of swim bladder inflation and caudal fin aspect ratio with reference to vertical distribution in Pacific bluefin tuna Thunnus orientalis larvae
2014
Ina, Y. (Kinki-Daigaku University, Nara (Japan). Faculty of Agriculture, Graduate School of Agriculture) | Sakamoto, W. | Miyashita, S. | Fukuda, H. | Torisawa, S. | Takagi, T.
It is necessary to understand the processes involved in sinking death in Pacific bluefin tuna Thunnus orientalis aquaculture in order to develop methods to prevent or minimize this problem. We observed the nighttime vertical distribution of Pacific bluefin tuna in the water column on 2-9 DAH and the morphological characteristics of the larvae, in order to clarify the processes involved in sinking death. A cuboid tank (height 300 cm) was used to measure vertical distribution. The number of larvae was counted in each of 4 regions in the observation tank: upper layer (water depth 0-100 cm), middle layer (100-200 cm), lower layer (200-300 cm), and bottom area. The distribution of larvae in these regions at 4 days after hatching was polarized to the upper layer and bottom area. Individuals with inflated swim bladders were observed in the upper layer 3 days after hatching. No larvae with inflated swim bladders were observed in the bottom area on any day after hatching. Total body length and caudal fin aspect ratio of larvae with both inflated and un-inflated swim bladders were greater in the upper layer than those of larvae in the bottom area. Larvae with un-inflated swim bladders that failed to develop sufficiently for swimming sank to the tank bottom and died. Swim bladder development and caudal fin swimming ability are strongly related to sinking death.
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