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Diseases of Aquatic Organisms

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DAO 44:61-68 (2001)  -  doi:10.3354/dao044061

Mass mortality of the Japanese pearl oyster Pinctada fucata martensii in relation to water temperature, chlorophyll a and phytoplankton composition

Yuji Tomaru1,*, Zen¹ichiro Kawabata2, Shin-ichi Nakano3

1Department of Environmental Conservation Sciences, The United Graduate School of Agricultural Sciences, and
3Center for Coastal Environmental Science Research, Ehime University, Tarumi 3-5-7, Matsuyama 790-8566, Ehime, Japan
2Center for Ecological Research, Kyoto University, Kamitanakami Hirano-cho 509-3, Otsu 520-2113, Japan
*Present address: Red Tide Biology Section, Red Tide Research Division, National Research Institute of Fisheries and Environment of Inland Sea, 2-17-5 Maruishi, Ohno, Saeki, Hiroshima 739-0452, Japan. E-mail:

ABSTRACT: Mass mortalities of the Japanese pearl oyster Pinctada fucata martensii have widely occurred in western Japan since 1994. The causes of these mass mortalities are at present not thoroughly understood. In this study, we investigated oyster survival in relation to some environmental factors such as water temperature, concentration of chlorophyll a and density or composition of phytoplankton. The examined mass mortality occurred from September to December 1998, and the color on the adductor muscle of the oysters was red-brown, suggesting an infectious disease. Oysters that became moribund during the experiment lost weight, while the weight of unaffected oysters increased. The cell density of Nitzschia spp., an inedible algae for the oyster, in Uchiumi Bay increased before and during the mass mortality event. From the results of our study, we hypothesize that P. fucata martensii was weakened by starvation because of the dominance of inedible food and then contracted an infectious disease that resulted in mortality.

KEY WORDS: Pearl oyster · Mortality · Water temperature · Phytoplankton

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