Reproductive cycle of two marine sentinel bivalve species (Donax trunculus and Scrobicularia plana) in the Agadir bay, Southern Morocco

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.