Détermination de la sexualité chez l'huître Crassostrea gigas (Thunberg, 1793)

ln France the Pacific oyster Crassostrea gigas has a great economical importance, its culture represents 150 000 t annually, approximately 210 million U.S. dollars. The aim of this work was to study the sexuality determinism of this species and contribute to the knowledge of its biology. The main objective was to define the sexuality at population and individual levels, and establish which are the external factors that influence the sex variation. This study was divided in three parts;(i) sexuality of a natural population from l'anse du Roz (bayof Brest -Finistère), (ii) the juvenile sex change along the time from oyster of the same location but cultivated at two different locations; la Pointe du Château (bay of Brest ..;.. Finistère) and Marennes -Oléron (Charente Maritime), and (iii) xperiments in relation of food and origin influence on sexuality carried out in laboratory conditions (IFREMER -La Tremblade and Brest). The results allowed us to establish that the reproductive cycle of C. gigas can be divided in four distinctive stages according to the physiological state (condition index), the oocyte development (oocyte diameter), and the seasonal temperature variations. Each stage was defined by a particular state using histological observations and modal analysis of oocyte diameters; early gametogenesis, growing, mature and degenerating stages. (...)