Recherches sur l'organisme responsable de la maladie des branchies

The first manifestations of an oyster disease were observed in France in November 1966 in Crassostrea angulata and in October 1967 in Ostrea edulis. The gills and palpi of the diseased molluscs showed rather numerous and large perforations and indentations. The tests for identifying the responsible organism that were attempted by the American researchers based on samples that were sent to them led them to suspect a ringworm, since this kind of infection is considered responsible, in the United States, for significant mortalities in oysters. It is in fact known that mushrooms can infest mollusc larvae in experimental breeds (Sirolpidium zoophtorum) and even the adults (Dermocystidium marinum); just as the epizootic that raged in Europe from 1919 to 1925 was also attributed to a mushroom. Nonetheless, we cannot discard a priori the possibility of a bacterial or viral infestation. That is why we have performed, in addition to extemporaneous microscopic observations of dilacerations with and without dye, many culture tests based on healthy and diseased oyster tissues in mycophilic and other media.