AbstractThe migratory behavior and spawning of Curimatá‐pacu (Prochilodus argenteus) were assessed in a free‐flowing remnant spanning approximately 450 km. This evaluation was conducted using radio‐tagging and egg sampling, with identification performed through metabarcoding techniques. Among the studied individuals, half migrated 100–365 km upstream, primarily in response to the initial rise in river discharge at the onset of the wet season. Conversely, the remaining fish did not exhibit upstream movement, indicating a partial migratory behavior. The presence of eggs exclusively in the headwaters suggests that breeding occurred solely among fish inhabiting the upstream sites. The observed migratory traits resembled those of other congeneric species.