Diet of the mangrove oyster crassostrea gasar (adanson, 1757) and plankton diversity in Lake Nokoué

The diet of the mangrove oyster Crassostrea gasar was studied in Nokoué Lake to provide data for oyster culture in south Benin. Specimens of C. gasar were collected monthly from July to September during the flood season. The stomach contents were analyzed as well as planktonic abundance. Planktonic organisms were collected using plankton net of 30 µm mesh size and observed under the microscope. In total, 102 stomachs were examined. The results showed that the diet of C. gasar is composed mainly of phytoplankton (96.04%) and zooplankton (1.80%). Among the phytoplankton organisms, the chlorophyte Stigeoclonium aestivale (44.86%) is the preferential food while Oscillatoria sp (Cyanophyte, 13.84%), Gyrosigma hyppocampus (diatom, 10.97%) and Lyngbya martensiana (Cyanophyte, 8.89%) are secondary foods. The other phytoplankton organisms are additional food items. Oyster diet composition showed significant variations between months and between class sizes. Moreover, data on planktonic composition of Lake Nokoué revealed that the diatom Aulacosira ambiga is the most predominant phytoplankton species. However, it was very little represented in the stomach; this indicates a selectivity in the diet of C. gasar.