Oocyte atresia in the Mangrove oyster, Crassostrea gasar (Dautzenberg 1891), (Bivalvia, Ostreidae) in tropical environment

Abstract

The mangrove oyster, Crassostrea gasar, is exploited in a natural state in the Casamance estuary in Senegal by rural women Diola. The decrease of its size on natural deposits and the remoteness of the harvesting areas, are at the origin of the Oyster culture project in Lower Casamance. It is in this context that the reproduction of the oyster, C. gasar in the Casamance estuary was studied between 1992 and 1994 to optimize its capture of its spats. Each month, a sample of about 30 adult oysters was collected at the same location in the Karabane region, 6 km from the mouth of Casamance. Of the thirty oysters monthly collected, 3-5 females were selected for study among larger individuals. A fragment of gonadal tissue was collected from each oyster and prepared for histological study: alcohol fixation, alcohol washing, dehydration, impregnation and paraffin embedding, cutting, staining, blade-slat assembly, and blade observation using a computer. A program has been installed to automatically calculate the occupation rate of the different oocytes observed. A large percentage of atretic oocytes are observed in follicles of the oyster gonad, within 04 months, before the main oyster reproduction period in the Karabane area. This situation would be caused when the reserves accumulated by the oysters during the gametogenesis of the oyster are insufficient in the quantity and quality of reserves accumulated by the oysters during the gametogenesis of the oyster.

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Keywords: mangrove oyster, reproduction, histology, atresia, Crassostrea gasar