Development of phototaxis in the early life stages of Pacific bluefin tuna Thunnus orientalis
2017
Ina, Y. (Seikai National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Nagasaki (Japan). Research Center for Tuna Aquaculture) | Sakakura, Y. | Tanaka, Y. | Yamada, T. | Kumon, K. | Eba, T. | Hashimoto, H. | Konishi, J. | Takashi, T. | Gen, K.
We investigated the development of phototaxis in larval and early juvenile stages of Pacific bluefin tuna Thunnus orientalis to detail behavior development in relation to light. We observed the distribution of Pacific bluefin tuna in an illumination gradient tank from 1 to 26 days after hatching (DAH). Two long rectangular tanks (100 * 10 * 10 cm) were used for experiments; each tank was divided into four sections for observations and one tank was equally illuminated at 1.0 * 10E3 lx as the control tank, and the other was at 4.0 * 10E2, 1.0 * 10E3, 1.0 * 10E4 and 7.0 * 10E4 lx as the illumination gradient tank. Laboratory-reared larvae and juvenile were released into each tank and acclimatized for 10 min. Thereafter, the number of individuals in each section was counted for 5 times with 10-min intervals. Until 2 DAH (3.6 +- 0.1 mm BL), larvae distributed homogeneously in each section in both tanks. After 3 DAH (3.7 +- 0.1 mm BL) when the eyes of the larvae were pigmented, most fish moved into the 7.0 * 10E4 lx section in the illumination gradient tank, while fish in the control tank maintained a uniform distribution during the experimental period (Chi-square test, P < 0.05). The results suggest that the post-larvae and juvenile stages show strong positive phototaxis.
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