Comparative growth of Bonamia ostreae resistant and wild flat oyster Ostrea edulis in an intensive system : II. Second year of the experiment

This paper reports the comparative growth and mortality of two crosses involving S85 and S89, two Ostrea edulis strains selected by IFREMER for their resistance to Bonamia ostreae. A first year of monitoring had revealed that the two crosses grew significantly better than two control populations from Quiberon Bay (Brittany) and Palavas (Mediterranean Sea). In a second and final year experiment which lasted from April to November 1995, the cross between the first generation of S89 and wild oysters (G0G1) performed better for most growth characteristics (whole weight, shell weight, length and width), than both the cross between the first generation of S89 and the second generation of S85 (G1G2) and the Quiberon control group, which were not significantly different from each other. Mortality was quite high during the experiment but was lower for the G0G1 cross (61%) than for both G1G2 (67%) and the Quiberon controls (76%). A low level of B. ostreae infection was detected during the experiments indicating early infections. These results are consistent with the previous one showing a direct or indirect effect of selection to B. ostreae resistance on growth.