Seasonal changes in the reproductive cycle and condition index of the surf clam Mactra stultorum (Mollusca: Bivalvia) in the Gulf of Gabes, Tunisia

The reproductive biology of Mactra stultorum from the Gulf of Gabes was investigated monthly during a oneyear period (2017). This study is the first study examining its reproductive biology during one-year in the south of Tunisia. The overall samples presented a balanced sex ratio, with males dominating among smaller individuals (< 22 mm) and females predominating in larger size classes (> 34 mm). The obtained total sex ratio (F:M) was equal to 1.03:1. The size at first maturity (SL50%) was 20.43 and 22.10 mm for males and females, respectively. The seasonal variations assessed through macro- and microscopic characteristics in the gonads of both sexes indicated a clearly defined annual reproductive cycle with a principal spawning peak during summer and a resting period during December and January. The reproduction of M. stultorum was strongly influenced by fluctuations in the seawater temperature, as reflected through the temporal variation in the gonadal cycle, condition index (CI) and tissue weight rate (TiWR). If managed properly, M. stultorum is expected to meet the domestic market demand through artisanal fishery. The adoption and implementation of rules, such as limiting the size of clams, is required to protect this new exploitable fishery resource.