The migratory histories of Cottus sp. (middle-egg type) were insighted from ontogenetic changes in otolith Sr:Ca ratios. We sampled 25 fish in the upstream and downstream of the Takase Weir in the Ota River. Twenty-four fish were categorized as amphidromous form whereas one individual caught in the upstream, showed landlocked life mode. Intraspecific variations in the migration pattern recorded for Cottus sp. (middle-egg type) suggest a plasticity strategy for diadromous behaviors.