Researchers are examining a possible 'intermediate host' among the more than 1,000 species which live in the oyster's vicinity. Molecular characterisation of the parasite has isolated a single European species, including a non-destructive variant in mussels. The relationship between hosts and parasites is currently being investigated. For over 15 years, researchers have attempted to launch flat oyster production again, endemically affected by two parasites, Bonamia ostrea and Marteilia refringens. One promising technique involves selecting resistant genitors in the natural environment and injecting massive amounts of purified parasites close to the heart.
Survivors are then cross-bred to obtain more tolerant animals.
These markers then allow better selection of tolerant genitors. A fifth generation of resistant flat oysters are being examined at the Ifremer La Tremblade station, increasing hopes of production of the species. Fortunately, research undertaken at the Ifremer station in La Tremblade has demonstrated that there is no genetic relationship between these herpes and those affecting humans and other mammals. Hybrids produced in laboratory conditions have been viable and fertile, with no preferential fecundity between the sperm of the two strains, proving they are of the same species. Other studies are attempting to determine if the importation of Crassostrea g. to the Iberian peninsula and France is resulting in the production of hybrids and impacting on the survival of 'pure' Portuguese strains, the subject of a future European project.