Bull. Jpn. Soc. Fish. Oceanogr. 81(3), Page 189-202, 2017   Geochemical analysis of otoliths for studying the migratory ecology of fishes Kazuki Yokouchi1, Yosuke Amano2, Toyoho Ishimura3, and Kotaro Shirai4† 1 National Research Institute of Fisheries Science, Fisheries Research Agency, 6-31-1 Nagai, Yokosuka, Kanagawa 238-0316, Japan 2 Tohoku National Fisheries Research Institute, Fisheries Research Agency, 3-27-5 Shiogama, Miyagi 985-0001, Japan 3 National Institute of Technology, Ibaraki College, 866 Nakane, Hitachinaka, Ibaraki 312-8508, Japan 4 International Coastal Research Center, Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan † E-mail: kshirai@aori.u-tokyo.ac.jp For the appropriate stock management of fish species, it is essential to investigate ecological information, such as species distribution and migration patterns. Recent studies have shown the usefulness of elemental and stable isotopic composition in fish otoliths as a natural tag for reconstructing the migratory ecology of fish. To provide guidance for the use elemental and stable isotopic composition of otoliths in ecological studies of fish, this study focuses on quantitatively describing the process and degree of variations of each chemical composition of otoliths, primarily by describing their geochemical aspects. The types of factors that are responsible for variations in elemental and stable isotopic composition of otoliths are discussed based on biological and latest geochemical findings. Additional detailed discussions are provided regarding things to be considered when interpreting data. Finally, some of our views are discussed as to the selection of optimal otolith elements and analysis methods required for providing new insights into the ecological studies of fish. Key words: stable isotope ratio, migratory fish, otolith, geochemistry, trace element