Bull. Jpn. Soc. Fish. Oceanogr. 73(2), Page 67-79, 2009   Natural behavior properties of adult Japanese flounder (Paralichthys olivaceus) in all season in the central western part of Seto Inland Sea Rena Shibata1†, Akihiko Takechi2*, Tatsuhiro Fukunaga3** and Akira Nitta4 1 Coastal Fisheries and Aquaculture Division, National Research Institute of Fisheries Science, 6-31-1 Nagai, Yokosuka, Kanagawa 238-0316, Japan 2 Ehime Prefectural Fisheries Experimental Station, 121-3 Iyo, Ehime 799-3125, Japan * Ehime Research Institute of Agriculture, Forestry and Fisheries, Fisheries Research Center, Research Institute of Cultivation Resources, 121-3 Iyo, Ehime 799-3125, Japan 3 Fisheries Research Agency, 2-3-3 Minatomirai, Nishi-ku, Yokohama, Kanagawa 220-6115, Japan ** National Association for the Promotion of Productive Seas, Chuo, Tokyo 103-0001, Japan 4 Japan NUS Co. Ltd., 3-9-15 Kaigan, Minato-ku, Tokyo 108-0022, Japan † e-mail: renas@fra.affrc.go.jp During late April (1998-2001) a total of 35 adult Japanese flounder, Paralichthys olivaceus, attached with archival tag, were released off Oshima Island, Seto Inland Sea. Of ten individuals recaptured after 19-688 days within a range of 40 km from the release point, seven had lost the archival tag. Tags of the remaining three individuals recaptured 299, 685 and 688 days after release contained a full 11 months of data. Differences in water temperature between the shallowest point and the deepest point were small (<1.0°C), despite vertical daily migrations of up to 102 m. We determined a depth change >2 m per 512 s period to be an indicator off bottom activity. Off bottom activity frequency (OBAF) was during 2.9 to 6.9% of the time recorded. OBAF was highest before and just after the spawning season (March-May), and lowest in the summer and early autumn. There was a high percentage of time spent swimming during both day and night after the spawning season, but only during the day before the spawning season. Since Japanese flounder often remain on the seabed and thus the depth recorded fluctuates with tidal conditions, it was possible to estimate the location of the fish position by matching the tidal information recorded in the tag with specific locations within the Seto Inland Sea. One fish was observed to move in the area off Oshima Island in Hiuchi Nada through the interisland area in Bingo Nada. The other two fish moved to the Aki Nada area, offshore of Matsuyama through the Kurushima Strait about 50 km west-southwest from the release point. One of these fish was captured off Kure, Hiroshima Prefecture; the other off Hojo, Ehime Prefecture. Key words: Japanese flounder, natural behavior, off bottom activity, Seto Inland Sea, archival tag