Gonadal changes and serum steriod levels during the annual reproductive cycle of the pearl oyster Pinctada fucata gould

The annual reproductive cycle of peal oyster Pinctada fucata was characteised by documenting gonadal development and changes in serum levels of estradiol-17b (E2), testosterone (T) and progesterone (P) in the wild bivalve caught in natural beds in the Persian Gulf throughout the year. Bivalve populations employed in this study spawn in June-July and November-December. The pearl oysters had group synchronous ovarian development with exogenous vitellogenesis during spring and summer for first spawning and during August-September for the second spawning. Serum E2 levels in the females increased rapidly from low values in May to peak in June and also in October coinciding with the time of spawning. Serum T levels in male and female exhibited a bimodal pattern. However in the male it increased during the early spermatogenesis. P was detected in both females and males. Its concentrations start to increase during the early gametogenesis and reaching to peak during the spawning season. The obtained results indicated that vitellogenesis and spermatogenesis in pearl oyster are not completed by the mi-summer and early winter.