Etude comparative de différents indices de condition chez l'huître creuse (Crassostrea gigas)

Among the different condition indices, some of them were compared on a population of the japanese oyster, Crassostrea gigas. The follow-up of experimental racks was performed monthly during four years. The use of dry weight in condition indices gave a more precise and more reliable representation for the condition of the oysters than the fresh weight. The sensitivity of these indices, which corresponds to their ability in revealing small changes in the physiological condition, was calculated for each indice. Those exhibiting the best sensitivity were ranked as follow: dry weight on the difference between total weight and shell weight, dry weight on intervalve volume. Other indices including the ratio between dry weight and various assessments of the volume (cube of the length, total volume, or products of length, width and thickness) and of the total' weight, has a lower, but similar sensitivity. Some criteria for selecting a condition indice according to its scientific or economic use were given. They were based on characteristics such as sensitivity, accordance with the biological events, and easiness of determination.