Seasonal variation in metabolism of cultured Pacific oyster, Crassostrea gigas, in Sanggou Bay, China

Rates of respiration and excretion of the Pacific oyster, Crassostrea gigas, were measured seasonally from June 2002 to July 2003 under ambient conditions of food, water temperature, pH, and salinity in Sanggou Bay, an important mariculture coast in north China. The aim of this study is to obtain fundamental data for further establishing an energy budget model and assessing the carrying capacity for cultivation of C. gigas in north China. Oysters were collected monthly or bimonthly from the integrated culture areas of bivalve and kelp in the bay. Oxygen consumption and ammonium and phosphorus excretion rates were measured, and ratios of O/N and N/P were calculated. One-way ANOVA was applied to determine differences among these parameters that act as a function of seasonal variation. All the physiological parameters yielded highly significant variations with season (P < 0.01). The rate of respiration varied seasonally, with the highest oxygen consumption rate in July and the lowest rate in January, ranging from 0.07 to 2.13 mg O2 h− 1 g− 1dry tissue weight (DW). Maximum and minimum ammonium excretion rates were recorded in August and January, respectively, ranging from 0.51 to 5.40 μmol NH4–N h− 1g− 1 DW. Rates of phosphorus excretion varied from 0.11 (in January) to 0.64 (in July) μmol PO4–P h− 1g− 1 DW. The O/N and N/P ratios changed from 9.2 (in January) to 59.8 (in July) and from 4.6 (in January) to 10.9 (in August), respectively. For each season, the allometric relationship between the physiological response (e.g., rate of oxygen consumption, ammonium and phosphorus excretion) and DW of the animal was estimated using the formula: Y = a × DWb.