Bull. Jpn. Soc. Fish. Oceanogr. 76(1), Page 1-8, 2012   High accumulation of manganese in the kidney of pen shell Pinna bicolor in Ariake Sea, Japan Chihiro Yamamoto1 † 1 Fukuoka Fisheries and Marine Technology Research Center Ariakekai Laboratory, 728-5 Yoshitomi-mach, Yanagawa, Fukuoka 832-0055, Japan †e-mail: trebuhcspf397@ori.bbiq.jp Pinna bicolor is a Pinnidae shellfish, inhabiting shallow waters from temperate to tropical zone. The bivalve possesses large kidneys filled with metal-rich granules. The concentration of manganese in dried kidney tissues of pen shells sampled from Ariake Sea, Hagi, and Kamigoto were 58,500 μg·g−1, 34,300 μg·g−1, and 5,700 μg·g−1, respectively. At the same time, manganese concentrations of 600 to 1,400 μg·g−1, 260 μg·g−1, and 130 μg·g−1 were found for sediment samples from Ariake Sea, Hagi, and Kamigoto, respectively. There were significant correlations between manganese concentration in the kidney and in the mud (p<0.01). These results suggest that manganese concentration in Pinna bicolor kidney can be an indicator of ionized manganese elution due to hypoxia or ooze deposition in the hydrosphere. Because the manganese concentration of samples at Ariake Sea was higher than ever reported. I assume that high elution of ionized manganese is occurring widely in the habitat of Pinna bicolor in Ariake Sea. Key words: Ariake Sea, Pinnidae, Atrina, Pinna bicolor, manganese, kidney