Graduate School of Bioresources, Mie University, Tsu, Mie 514-8507, Japan
The seaward migration period of anadromous Japanese dace Tribolodon hakonensis in the Kamo River was surveyed by periodical changes of occurrence at two stations: their spawning area (freshwater) and lower tidal area (brackish). Except when spawning occurred, only age 0 and 1 fish were collected. Both age 0 and 1 fish appeared in the tidal area from spring to summer and the number of individuals caught per minute in the spawning area concurrently decreased. These results indicate that the seaward migration period of T. hakonensis in the Kamo River is from spring and summer at age 0 and 1. Based on otolith Sr:Ca ratio analysis, specimens initially migrating into the tidal area were estimated to be 12 to 106 mm standard length.