RARE KEY SUBSTANES OLFACTORY SENSE : IDETIFICATION OF HOME STREAM SUBSTANCES IN SALMON

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Salmon have the amazing ability to migrate long distances from the ocean to their home streams for spawning.For open water orientation, we showed that salmon use visual cues. For upstream homing from the coastal area to the home stream, the olfactory hypothesis has proposed, but the odor substances of home stream are unknown.In the previous study, we proposed that the odor substances are amino acids.The present study aims to prove this hypothesis.Upstream selective movements of chum salmon (Oncorhynchus keta), which were captured in the Osaru Rive, Hokkaido, Japan, in late spawning season, was investigated in a two-choice test tank consisted of two water inlet arms and one pool. Artificial home stream river water and lake water were added to each arm. Artificial home stream water was prepared based on the compositions of amino acids and related substance of the Osaru River. Mature male chum salmon were captured by the wire in the Osaru River, Hokkaido, and transferred to the Toya Lake Station, Hokkaido University. Of chum salmon tested, 28 fish showed upstream movement to one of the choice arm, and 24 fish (85.7%) of those moved fish were found in the arm running the artificial home stream water.These results strongly support our hypothesis that amino acids disslved in stream waters are home stream substances for salmon homing.