During this period, the water temperature was below 16☌. ![]() An initial increment in the number of PCR-positive oysters was reported at both field sites during the survey in the absence of significant mortality. Mass mortality was observed among oysters a few days after increases in the number of PCR-positive oysters and viral-DNA amounts were recorded. This difference may be related to earlier increases in water temperature. Although similar massive mortality rates were reported at the 4 sites, mortality was detected earlier in the pond and in the nursery than at both field sites. Mortality rates were recorded based on regular observation, and samples were collected to search for and quantify OsHV-1 DNA by real-time PCR. For this purpose, a single batch of Pacific oyster spat was deployed in 4 different locations in the Marennes-Oleron area (France): an oyster pond ("claire"), a shellfish nursery, and two locations in the field. Additional data are necessary to better describe mortality events in relation to environmental-parameter fluctuations and OsHV-1 detection. gigas in Europe have been related to the detection of a variant of OsHV-1 called μVar. Since 2008, mass mortality outbreaks among C. This virus has been classified as Ostreid herpesvirus 1 (OsHV-1) within the family Malacoherpesviridae. A particular herpesvirus was purified from naturally infected larval Pacific oysters, and its genome was completely sequenced. N2 - A number of bivalve species worldwide, including the Pacific oyster, Crassostrea gigas, have been affected by mass mortality events associated with herpesviruses, resulting in significant losses. JF - Applied and environmental microbiology T1 - Ostreid herpesvirus 1 infection among Pacific oyster (Crassostrea gigas) Spat: relevance of water temperature to virus replication and circulation prior to the onset of mortality. Possible reasons why a high genetic variance for survival appears to be maintained in wild populations are discussed.A number of bivalve species worldwide, including the Pacific oyster, Crassostrea gigas, have been affected by mass mortality events associated with herpesviruses, resulting in significant losses. As yield mostly depends on survival and growth, this approach should significantly improve harvestable yield. Selective breeding in a single site should therefore be an efficient means of improving survival in oysters less than one year old along the French Atlantic and Channel coastlines with only very limited effects on growth. Finally, genetic correlations between growth and survival were low, in all sites. In contrast, lower genetic variation was observed for growth in all sites. Genetic correlations across sites were positive and very high for survival, indicating no genotype by environment interaction. A strong genetic basis was found for survival as narrow-sense heritability estimates ranged from 0.47 to 1.08, with higher values in sites where summer mortality was higher. As part of the MOREST project, 43 full-sib families nested within 17 half-sib families were produced, planted out and tested in 3 sites during summer 2001 to assess to what extent genetic variability exists for this trait. ![]() The multidisciplinary project “MOREST” aims to improve our understanding of causes of summer mortality in Crassostrea gigas juveniles in France and to reduce its impact on oyster production.
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