Darkness represses the onset of downstream migration in hatcheryreleased chum salmon, Oncorhynchus keta, fry
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Downstream migration and plasma thyroxine (T4) levels in hatchery reared chum salmon, Oncorhynchus keta, fry were investigated late in the migration season. Groups of 1.7.6.7 million fry were discharged by opening gates of the raceways at 09:30 h for a daytime release and at 18:30 h for a nighttime release experiments. A peak in the number of migrating fry and T4 surge were detected simultaneously, 1.1.5 h after the release in the daytime release. In nighttime release, the peak of T4 surge occurred 3 h after the release, and the number of the migrating fry peaked 8 h and 11 h after the release. In dark treatment, although the control group showed peaks within 2 h of the gate opening, the downstream migration of the dark-treated fish was repressed in daytime and small number of migrating fish was observed 3 h and 10 h after the gate opening, These results suggest that darkness represses the onset of downstream migration in chum fry late in the migration season, and the T4 surge is not related to the onset of downstream migration during the night.
- International Coastal Research Center, Ocean Research Institute, the University of Tokyoの論文
International Coastal Research Center, Ocean Research Institute, the University of Tokyo | 論文
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- Darkness represses the onset of downstream migration in hatcheryreleased chum salmon, Oncorhynchus keta, fry