Abstract
The reproductive cycle of two marine sentinel bivalve species, Donax trunculus and Scrobicularia plana, was studied from monthly random samples. A total of 1200 specimens were collected from January to December 2019 in two different sites of Agadir bay (Agadir beach; AG and Oued Souss estuary; OS). The analysis was based on the temporal variation of condition index, gonadal index, sex-ratio, and maturity stages of gonads through histological observation. We also studied the environmental parameters and their impact on the reproduction of those species. Results indicate that the sex-ratio was slightly unbalanced in favor of females in AG (▪= 1: 1.3) and males in OS (▪= 1: 0.9). Stages of gonad development maturity were identified as five stages: undifferentiated, developing, ripe, spawning, and spent. The spawning period occurred from March to July for S. plana, and from May to August for D. trunculus; the two species had one annual gonadal cycle. During the microscopic observations, no parasitic infection was detected. The physico-chemical parameters; especially temperature, dissolved oxygen, pH, and precipitation, influenced the gonads maturity and the spawning process in the studied species.
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