Bull. Jpn. Soc. Fish. Oceanogr. 77(2), Page 59-67, 2013   Sexual maturation, spawning period and batch fecundity of Japanese sardine Sardinops melanostictus in the coastal waters off western Japan in 2008-2010 Michio Yoneda1a †, Hiroshige Tanaka2b, Satoshi Honda1, Hiroshi Nishida1c, Kazuya Nashida1, 3, Yuichi Hirota1, 3, Minoru Ishida3d, Seiji Ohshimo2, Shin Miyabe4e, Haruka Ito1 and Akio Shimizu1 1 National Research Institute of Fisheries Science, 2-12-4 Fukuura, Kanazawa, Yokohama, Kanagawa 236-8648, Japan 2 Seikai National Fisheries Research Institute, 1551-8 Taira, Nagasaki, Nagasaki 851-2213, Japan 3 National Research Institute of Fisheries Science, Kochi Station, 6-1-21 Sanbashidori, Kochi, Kochi 780-8010, Japan 4 Tottori Prefectural Fisheries Experimental Station, 107 Takenouchidanchi, Sakaiminato, Tottori 684-0046, Japan a Present: National Research Institute of Fisheries and Environmental Inland Sea Hakatajima Station, Kou-2780 Hakata, Kinoura, Imabari, Ehime 794-2305, Japan b Present: Hokkaido National Fisheries Research Institute, 116 Katsurakoi, Kushiro, Hokkaido 085-0802, Japan c Present: Fisheries Agency, Ministry of Agriculture, Forestry and Fisheries, 1-2-1 Kasumigaseki, Chiyoda, Tokyo 100-8907, Japan d Present: National Research Institute of Fisheries and Environmental Inland Sea Tamano Station, 5-21-1 Chikkou Tamano, Okayama 706-0002, Japan e Present: Tottori Prefectural Government Kansai Office, 1-1-3-2200 Umeda, Kita, Osaka, Osaka 530-0001, Japan † E-mail: myoneda@fra.affrc.go.jp We examined the sexual maturation, spawning period and batch fecundity of Japanese sardine Sardinops melanostictus collected from coastal waters off Kochi Prefecture （KP）, northwestern Kyushu （NWK）, and the San-in district （SD） during the 2008-2010 period of low stock abundance to understand the reproductive characteristics of the current stock biomass. All male specimens were mature in all age classes examined in the three locations. Similarly, most females in these locations were mature although inter-annual variation in the percentage of mature 1-year-old females was found in SD in association with differences in the body length and relative condition factor of individuals. Monthly changes in ovarian condition showed differences in the peak spawning period among sampling locations. The relative condition factor of females in the three locations decreased and reached a minimum at the peak spawning period, thereafter it increased from the late spawning period. Spatial variation in the relative condition factor of mature females was evident as females in SD had a better condition than those in KP and NWK. There were no significant differences in the relative batch fecundity between specimens at age 1 and 2+ years and among the three locations. These findings indicated that the majority of 1-year-old specimens off western Japan matured and spawned in contrast to the evidence found during the past time of higher and lower stock abundance. Key words: age at maturation, batch fecundity, condition factor, Japanese sardine, spawning season, stock fluctuation