Histological identification of the gonadal phases of the European oyster (Ostrea edulis), introduced experimentally into the north western coast of Baja California, Mexico.
Five gonadal phases were identified by monitoring monthly gonadal changes from Feb. 1984 to Jan. 1985. These were (1) an indifferent phase, during Feb.-Mar., characterised by the presence of small empty follicles, (2) a gametogenic phase, mainly in Feb., characterised by large quantities of ♂ and ♀ sex cells in different stages of development, (3) a mature phase, in May-July, in which the follicles were swollen and full of well-developed gametes, (4) the spawning phase, from May-Aug., in which the follicles were disrupted, and (5) the postspawning phase, in Sep.-Nov., in which the follicles were small and contained a large number of phagocytes and undischarged sex cells. It was concluded that, under the conditions of this study, Ostrea edulis exhibited continuous gametogenesis and did not have the period of gonadal inactivity in winter (Jan.-Mar.) that is observed in this species in other parts of the world.