Monthly variation of biochemical composition of Pacific oysters Crassostrea gigas from two main cultivation areas in Japan

Pacific oysters were harvested from November to March at Miyazaki and Miyagi in Japan. From biometric analysis, the condition indices (CICG; high CICG indicates large oyster meat) of oysters were high in February and March at Miyazaki whereas CICG at Miyagi showed high values in December and February. Lipid content in oysters at Miyagi harvested in February was the highest. Glycogen content was high in oysters harvested in February from both cultivation areas. In November, the calcium content in oysters harvested at Miyazaki was the highest. Taurine was the predominant free amino acid in oysters, at concentrations of 2180–3230 mg/100 g dry sample. Glutamate was the predominant component of total amino acid in oysters, at concentrations of 4530–6000 mg/100 g. The percentage of eicosapentaenoic acid (EPA) in total lipid of oysters did not show significant differences between harvesting months. Based on all analyses, oysters from Miyazaki showed good quality in March with high CICG, glycogen, and lipid contents, whereas oysters from Miyagi showed good quality in February. These analysis data including not only condition indices but also biochemical composition might be useful parameters allowing establishment of evaluation criteria.