Humans have long been fascinated by the mysteries surrounding fish migrations, and addressing these complex behaviors often requires large datasets. Biogeochemical tags, including trace elements and stable isotopes, are the most accessible biomarkers for tracking fish migrations. However, access to standardized biogeochemical tag data is rarely available for migratory fish, which limits our understanding of the evolutionary origins, drivers, timing, and corridors of migration. This precludes the development of conservation strategies and the implementation of management actions. Here, we present MFishBT, a global, open-access database of Migratory Fish’s Biogeochemical Tags. As of April 2023, the MFishBT contains biogeochemical records from 1,305 studies, of which 53% used element-to-calcium (E/Ca) ratios, 34% used isotopic ratios, and 13% used both techniques. The database covers 17,402 field sampling locations (inland 47% vs. marine 53%) around the globe, comprising 490 migratory fish species of four classes, 44 orders/suborders, and 137 families. Seventy-nine trace elements and 12 isotope systems were measured across various fish biomineral archives, including otoliths, scales, eye lenses, and vertebrae. E/Ca ratios were examined more frequently than isotopic ratios (59% vs. 41%), led by Sr/Ca, Mg/Ca, Ba/Ca, and 87Sr/86Sr, δ13C, and δ18O, respectively. The MFishBT compiles 26,417, 15,628, and 2,450,571 records with biogeochemical element values detected in the cores, edges, and core-to-edge transects for biomineral archives of migratory fish, respectively. This is the most globally comprehensive open-access database on biogeochemical tags in migratory fish to date, which can serve a variety of needs in scientific research, conservation, and management. We encourage researchers to add more datasets to this database in the future. This database is released for non-commercial use only. There are no copyright restrictions, and please cite this paper when using these data, or a subset of these data, for publication.

MFishBT(https://fish-ecology.shinyapps.io/mfishbt) MFishBTdat(https://github.com/Otoliths/MFishBTdat)