La maladie des branchies chez les huitres du genre Crassostrea caracteristiques et evolution des alterations processus de cicatrisation

A few observations were mentioned in an earlier paper (COMPS, 1969) that concerned the histological features of the lesions that appeared during the gill infection to which Crassostrea angulata has been particularly prone since 1966. Since it has, however, not been possible to date to isolate and grow a culture of the parasite presumed to be the responsible agent of the disease, a more complete anatomopathological and histological study was contemplated in order to try to specify the definition of the offending protist and reveal the process of deterioration of the oyster's tissues as well as the reactions of the host to the infestation by and growth of the parasite. In addition, importing Crassostrea gigas THUNBERG from Japan at the very moment that gill disease was rampant in Crassostrea angulata in France led to screening of samples taken from batches of Japanese oysters before their immersion in the waters of the various French oyster farming basins (l). Similar screenings were moreover done on oysters of the same species imported from Korea and British Columbia. The whole of the observations conducted had made it possible to establish that the imported oysters had lesions identical to those found in C. angulata and in quite varying proportions as noted by MARTEIL (1968). The average rates of infected C. gigas, for the year 1968, were the following: oysters imported from Japan: 27%, from Korea: 56%, from British Columbia: 14%. MARTEIL had furthermore pointed out that among the screened oysters, severe attacks (stage 3) were lacking. Considering the screenings done to this day and the resulting data, it seemed worthwhile, in relation to the known elements of the gill distortions of Crassostrea angulata, to specify the anatomical and histological features of the indented gills in C. gigas. In short, this research work was complemented by an experimental study of lesions artificially made on Portuguese oysters' gills. In fact, whereas the infection in question can at the extreme lead to the death of the subjects, it is certain that a number of infected individuals react to the tissue erosion; in particular, the phenomenon of reactive hyperplasia may occur, as pointed out by BESSE (1968). However, whereas we were able, based on microscopic sections, to define features representing a "mending" of the tissues, it also seemed useful to show in what measure and according to what methods the oysters is likely, even before regenerating its gills, to react, even if only by simple healing, to the lesions that it can sustain in one way or another. It is with this goal that the question was contemplated experimentally just as was done by ATKINS (1930) in the context of a study focusing on regeneration of gills in the Mytilus edulis LINNÉ.