Amino acids in stream water are essential for salmon homing migration

Upstream selective movement of chum salmon (Oncorhynchus keta), which were captured in the Osaru River, 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 water that was prepared based on the compositions of amino acids and related substances of the Osaru River, and natural lake water flowed in each arm. Of 44 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. When the artificial home stream water flowed from the left and right arms, 88.9% and 80% of fish were observed in the left and right arms, respectively. These results strongly support our hypothesis that amino acids dissolved in stream waters are home stream substances for salmon homing.