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Fig. 21. Schematic drawing of three-step raceway that consists of upper, middle, and lower ponds. This raceway enables us to quantify upstream and downstream swimming behaviors at the same period. After the experimental fish had been reared in tanks, they were transferred to the middle pond (4 × 2 × 0.5 m) of the raceway. The middle pond was connected to the upper (4 × 2 × 0.5 m) and lower (4 × 2 × 0.5 m) ponds through square holes (50 × 25 cm, thickness 3 cm) which were made on wooden walls. Flow rate (volume) and velocity of the water in the raceway were 10 l/s and 75-85 cm/s. The upstream and downstream migrants are identified when the fish swam from the middle pond to the net traps (2 × 0.7 × 0.7 m) that were located in the upper and lower ponds, respectively. Reprinted from Aquaculture (in press), Munakata et al., Involvement of sex steroids and thyroid hormones in upstream and downstream behaviors in masu salmon, Oncorhynchus masou, © 2012a, with permission from Elsevier.

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