| Popis: |
A number of studies have investigated the amazing abilities of salmon to migrate long distances from the ocean to their natal streams for spawning, but much remains unknown because of the difficulties in following the whole life cycle, especially the oceanic migration. Kokanee Oncorhynchus nerka (lacustrine sockeye salmon), offer promise as systems for studying the physiological mechanisms of homing ability in salmon. Three types of physiological study, from behavior to molecules, were conducted using Lake Toya and Lake Shikotsu, Hokkaido, Japan, as model "oceans" and are reviewed here. The first study examined homing behavior of mature sockeye salmon in Lake Toya using ultrasonic tracking systems, testing for use of visual cues and magnetic orientation. Visual cues, but not magnetic orientation, appeared to be important in straight homing behavior. The second study examined the effect of hormonal controlling mechanisms, in relation to sexual differences, on homing duration (the time required to home) and homing accuracy during the spawning season in Lake Shikotsu. Administering gonadotropin-releasing hormone (GnRH) analog shortened homing duration. The third study examined the olfactory discriminating ability of home stream odorants using a twochoice test tank. Sockeye salmon exhibited preferential upstream selective movement toward artificial home stream water that had been prepared to mimic the composition of amino acids and related substance of the home stream. These results demonstrate the suitability of the lacustrine model for studying the physiological mechanisms of homing ability in sockeye salmon. |
