To reveal the life history pattern of Shirauo, Salangichthys microdon, in Lake Ogawara, we examined otolith Sr:Ca ratios in individuals from Lake Ogawara (n=12) and its tributary, the Takase River (n=6). Sr:Ca ratios were observed in two types of patterns: a resident pattern with low Sr:Ca ratio from core to edge, and an anadromous pattern with abrupt increases in Sr:Ca ratio. Back-calculated total lengths at the time of seaward migrations of anadromous individuals were 63.4-67.7 mm for five specimens from the river, and 36.8-63.8 mm for three from the lake. These findings suggest there is a wide variation in life history for S. microdon, and that residents and anadromous migrants live together in the lake.