A comparative study of the ecophysiology of the cupped oysters Crassostrea gigas, Crassostrea angulata and their hybrids was carried out in January 2000. Progenies were obtained by crossing parental oysters that had been previously identified using a diagnostic mitochondrial genome marker. Thus, two pure progenies were obtained by crossing within C. angulata parents (AA) or C. gigas parents (GG). Two other progenies were produced by hybrid crossing of C. gigas females with C. angulata males (GA), or C. angulata females with C. gigas males (AG). Individual measurements of the ecophysiology of 35 animals from each progeny were carried out at 19±1 °C. The oysters were fed Skeletonema costatum. The means of clearance and oxygen consumption rates obtained from continuous data recording over 3 h did not reveal differences between the four lines. However, the feeding time activity (FTA) results showed significant differences: for AA, GG, GA and AG animals FTA were 73±10%, 89±6%, 89±7% and 85±8%, respectively. The FTA of the AA progeny was significantly lower than the three other lines. This study shows that FTA is an ecophysiological parameter that can account for observed differences in growth. The ecophysiological measures should now be completed by a study to determine the optimum temperature for each oyster taxon.

Clearance and oxygen consumption rates of Ostrea edulis were measured at different temperatures (10-30 degrees C) in individual animals of a total weight ranging from 5 to 120 g (0.1 to 2.7 g dry tissue weight), outside the period of gametogenesis. For each temperature, the allometric relationship between the physiological response and dry tissue weight of the animal (DW) was estimated using the formula: Y = a * DWb. A statistical model is proposed for the variation in clearance rate or oxygen consumption rate (Y) with temperature (T) and DW: Y = [a + (b * c(T))] * DWd. The calculated value for d was 0.62 for clearance rate and 0.74 for oxygen consumption rate. The rates of both physiological functions increased as the temperature increased and reached maximum levels at 30 degrees C (clearance rate:2.83 +/- 0.32 1 h(-1) g(-1) oxygen consumption rate: 1.78 +/- 0.23 mg O-2 h(-1) g(-1)) when the flat oysters were fed a Skeletonema costatum microalgal grown in underground seawater. (C) 1998 Elsevier Science B.V. All rights reserved.