Bull. Jpn. Soc. Fish. Oceanogr. 78(1), Page 13-27, 2014   Effects of artificial upwelling on the environment and reared oyster Crassostrea gigas in Omura Bay, Japan Darien Danielle Mizuta1†, Akihide Kasai2, Ken-Ichiro Ishii1, Hitoshi Yamaguchi3 and Hideaki Nakata4 1 Graduate School of Agriculture, Kyoto University, Oiwake, Kitashirakawa, Sakyo, Kyoto 606-8502, Japan 2 Field Science Education and Research Center, Kyoto University, Oiwake, Kitashirakawa, Sakyo, Kyoto 606-8502, Japan 3 Nagasaki Prefectural Institute for Environmental Research and Public Health, 2-1306-11, Ikeda, Ohmura, Nagasaki 856-0026, Japan 4 Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, 1-14 Bunkyocho, Nagasaki 852-8521, Japan † E-mail: d.danim@hotmail.com Artificial upwelling was tested at Seihi, Omura Bay, Nagasaki Prefecture, as a way to improve environmental conditions for Pacific oyster farming. Aeration was performed from the sea bottom during two summer seasons in 2011 and 2012. Oceanographic parameters (temperature, salinity, dissolved oxygen concentration, chlorophyll a concentration, and suspended solids) and oyster performance (growth, survival, condition index, and glycogen levels) were monitored monthly. Aeration was shown to be efficient in improving water conditions for oyster farming, especially in the beginning of summer, by locally lowering water temperature by approximately 1°C, redistributing nutrients, and increasing diatom biomass. Dissolved oxygen concentration increased from October, at the beginning of autumn. The condition index of oysters was negatively related to distance from the aeration point. Furthermore, a reproductive season occurring when the aeration could not overcome high temperatures and formation of hypoxic water resulted in poor oyster health (condition index and glycogen levels decreased in September). Our results indicate that aeration can improve bivalve cultures if it is performed at a rate that overcomes hypoxia formation and high water temperatures throughout the summer period. Key words: hypoxia, enclosed bay, artificial upwelling, Pacific oyster culture, condition index