Bull. Jpn. Soc. Fish. Oceanogr. 75(1), Page 1-8, 2011   Age, growth and reproductive characteristics of yellowtail (Seriola quinqueradiata) caught in the waters off western Kyushu Tetsuro Shiraishi1*, Seiji Ohshimo1 and Ryuji Yukami1 1 Seikai National Fisheries Research Institute, 1551-8 Taira-machi, Nagasaki, Nagasaki 851-2213, Japan * Oita Prefecture Public Fisheries Corporation, 1006-1 Tsurukawa, Kunisaki-machi, Kunisaki, Oita 873-0503, Japan   † yukami@affrc.go.jp Growth and reproductive characteristics of yellowtail, Seriola quinqueradiata, collected off western Kyushu from February 2003 to April 2007 were determined based on vertebral centrum readings and gonad histology. The formation pattern on the centrum surface was distinct, and opaque zones (annuli) were visible. There is no significant difference in the von Bertalanffy growth parameters between males and females, and the combined growth model was FLt=1042 [1-exp {-0.311 (t+0.988)}], where FLt is the fork length (mm) at age t (years). The spawning period was estimated from March to May in the study area based on the results from monthly changes in the gonadosomatic index and maturity stage composition. Maturation body size (FL) and age were estimated to be 605 and 632 mm for male and female, respectively, and 2 years old for both sexes. Key words: centrum, first maturation, growth, spawning period, yellowtail, Seriola quinqueradiata