he present study aimed to describing the annual reproductive cycle of this species using gonadal tissue indicators. In this research, about 120 samples of sea urchin E. mathaei (60 female and 60 male samples) were collected monthly (about 10 samples/month) between February 2023 and January 2024 from the tidal zone of Bushehr coasts, situated at the north of the Persian Gulf. After removing the external hard shell, the gonads were separated from the body. 5 to 6 μm tissue sections were prepared using histological techniques, and stained with hematoxylin and eosin (H&E). Then, the gender of the samples, different stages of sexual maturity, the mean gonadal index, the gonad coverage area, the frequency of
oocytes in different stages and the diameter of oocytes were determined. Six stages of sexual maturity, including repair, growing, premature, mature, spawning and reabsorption stages, were detected in the gonads of male and female E. mathaei. Only one annual reproductive cycle was identified for this species. In the female, this cycle included a period of gametogenic activity (from December to June), a spawning period of several months (from June to August), followed by a long period of recovery and sexual rest (from August to the end of December). In males, the period of gametogenesis started from October and lasted until the end of May. It was followed by the spawning period from June to August and then a short period of recovery and sexual rest (September). It seems that the decrease in water temperature stimulates the start of the gametogenic cycle and the high values of sea water temperature stimulate the release of gametes of E. mathaei in Bushehr. It was found that the month followed the spawning period from June to early September. After that, the reabsorption period started from September. The highest values of the mean gonadal index and the gonad coverage area were belonged to samples collected in June and May with the peak in June. The lowest level of these