Comparative study of reproduction cycle of mangrove oyster (Crassostrea gasar) of the lagoons Ebrie and Aby (Côte d'Ivoire)

This study aims to give the bases of an efficient management of oyster stocks of the lagoons of the Ivory Coast and further bases of oyster-farming. It characterizes the reproduction cycle of mangrove oyster Crassostrea gasar in two lagoons of Côte d’Ivoire. The Ebrié lagoon; on the level of Grand-Bassam and Azito and the Aby lagoon; on the level of Assinie. Thus, a monthly sampling of 30 oysters per site for 12 months (October 2015 at September 2016) has been made. For each oyster, the linear and ponderal parameters were determined. In addition, the gonad of each oyster was extracted and subjected to a histological study. The results showed that C. gasar has a cycle of reproduction made up of five (5) stages sexual maturity. The sex-ratio is in favour of the females with respectively the ratio (male/female) of 1:2.9 ratios in Assinie, 1:4 in Grand-Bassam and 1:2.6 in Azito. It was noted that C. gasar has a continuous reproduction. However, stages III and IV were more present during the small rainy season (SRS) and the small dry season (SDS) at the level of the sites of Assinie and Grand-Bassam. It is during these two seasons that the gonadosomatic index and the condition factor had its greater values. As for the site of Azito, it recorded constancy in the evolution of gonadosomatic index and the condition factor. At the end of this study, it would be interesting to consider the culture of the mangrove oysters (C. gasar) in an environment controlled to ensure the perennity.