Bull. Jpn. Soc. Fish. Oceanogr. 83(2), Page 87-92, 2019   Age in days and growth of juvenile yellowtail, Seriola quinqueradiata, caught in waters off Kagoshima Prefecture, southwestern Japan Hirotoshi Shishidou1†, Shizuha Mizuno2 and Teruhisa Komatsu2,3 1 Kagoshima Prefecture Fisheries Technology and Development Center, 160–10 Iwamoto, Ibusuki, Kagoshima 891–0315, Japan 2 Atmosphere and Ocean Research Institute, The University of Tokyo, 5–1–5 Kashiwanoha, Kashiwa, Chiba 277–8564, Japan 3 Faculty of Commerce, Yokohama College of Commerce, 4–11–1 Higashiterao, Tsurumiku, Yokohama, Kanagawa 230–8577 † E-mail: shishidou-hirotoshi@pref.kagoshima.lg.jp We are developing a system to estimate a migration period of juvenile yellowtail (Seriola quinqueradiata) in waters off Kagoshima Prefecture. As a part of this research, ages in days and growths of juvenile yellowtail associated with floating seaweeds were examined with an analysis of otolith daily increments. Sagittal otoliths were obtained from 343 juvenile yellowtails caught in waters off Kagoshima Prefecture in March and April from 2010 to 2012. The analysis suggested that ages in days of specimens were between 22 and 69. By grouping specimens into collection month groups of each year, birth months of those collected in March and April were estimated to be from mid-January to mid-February and early February to mid-March, respectively. Growth rates of the specimen groups in order starting with the fastest were in April of 2012, April of 2011 and 2012, and March of 2010 to 2012. The slowest growth rate was in March of 2010 to 2012 in this study, and greater than that reported in the previous study on growth rates of juvenile yellowtail collected in May 1992 around Goto Islands in the East China Sea. It is estimated that growth rates of juvenile yellowtail groups by months and areas are positively related to their water temperature environments, which they experience, depending on their hatching periods and growing areas. Key words: juvenile yellowtail, otolith increments, age in days, growth