A total number of 2024 individuals of purple sea urchin Paracentrotus lividus was collected on monthly basis during the years 2017-2020. The specimens were collected manually by scuba diving from locations close to the coastline off Alexandria City . The main objective of this study was to describe the gametogenic cycle, sex ratio and size at first sexual maturity of P. lividus from the southeastern Mediterranean, off Alexandria coast, Egypt.
Four different maturity stages were recognized after histological analysis of both female and male gonads ( stage I: Recovery, stage II: Growing, stage III: Mature, and stage IV: Spent) (Fig. 1) . In our study, the gametogenesis cycle (stage I and II) began in Jan and reached its peak in Mar followed by a release of the mature gametes during Apr and May. Afterwards, there was a high abundance of nutritive phagocytes from Jun to Aug . Generally, the gametogenic cycle of the Egyptian P. lividus population off Alexandria Coast reveal two incidences of spawning where gonads become in the stage of development, maturation, ripening and spawning during late autumn and early winter and mid-winter and late spring, then they become resting and in the stage of recovering during the summer months.
The sex of sea urchins was examined by the macroscopic examination or with a smear examination, and the sex-ratio (?/?) was determined. The result of the chi-square test showed that there is a significant difference in sex ratio from a 1:1 ratio among different months. In the months Mar, May, Aug, Sep, Oct & Dec 1:1 sex ratio was observed, while in the months of Jan, Feb, Apr, Jun, Jul & Nov the sex ratio was in favor of the males (1: 1.2).
In order to determine the size at first sexual maturity of P. lividus a subsample of 416 individuals was analyzed histologically . The recovery stage was considered immature, while the 3 remaining stages; the growing, mature and spent; were grouped and considered the mature stages. In males, the smallest observed mature individual had 19.10 mm test diameter (TD) and the calculated L50 was reached at 20 mm. For females, the smallest observed mature individual had 22.70 mm TD and the calculated L50 was reached at 20 mm. As L50 for both males and females were equal then both sexes reach maturity simultaneously. This study may help in the regulation of the fis heries of P. lividus to protect its natural stock from over-exploitation.