Seasonal Variation in the Chemical Composition and Condition Indices of Pacific Oyster, Crassostrea gigas, Grown in Trays or on the Sea Bed

Abstract

Chemical composition and condition indices of tray and bottom-cultured Pacific oyster, Crassostrea gigas, were measured and compared over a 13-mo period. Tray oysters were less dense than bottom oysters as a result of increased porosity of shells. Dry meat condition indices were slightly higher in oysters grown in trays. Chloride and iodide levels peaked in early spring. Minor seasonal deviations occurred from the mean 61.0% polymeric matter, 31.5% hydrophilic matter of low molecular weight, and 7.5% lipid matter in both groups of oysters. Nonprotein to protein nitrogen ratio in tray and bottom oysters averaged 0.37 and 0.35, respectively, throughout the season. A procedure was developed to assess glycogen in situ in polymeric material fractionated from meat. Glycogen averaged 79.5 and 79.0% of the total glucose in tray and bottom oysters, respectively; the remainder consisted of the homologous series of α(1 → 4)-linked D-glucose oligomers. Degree of polymerization of oligosaccharides in tray and bottom oysters averaged 2.93 and 2.91, respectively. Dry meat condition indices correlated predominantly with protein condition indices, only secondarily with glycogen condition indices and insignificantly with the remaining constituent condition indices of tray and bottom oysters.Key words: Crassostrea gigas, tray and bottom cultures, chemical composition, nitrogen, carbohydrates, halides, density, condition indices, seasonal variations