Occurrence of phytoplankton in the water and gut of the volta clam (Galatea paradoxa born 1778) from the lower volta estuary, Ghana

Abstract

The Volta Clam, Galatea paradoxa Born 1778 (= Egeria radiata) occurs in the waters of the Lower Volta Estuary. It is an important source of protein for the inhabitants and fishing for clams is done to supplement income. The clam is eaten whole after frying, boiling, steaming or roasting. The gut contains many microalgae that are resident in the enclosing riverine water. This paper reports the incidence of microalgae (phytoplankton) in the surrounding water and in the gut of the clam with the view to identifying potential toxin-producing ones which constitute the phytoplankton population. The phytoplankton content of the riverine water and in the gut ofthe clam was determined using standard and prescribed methods. Out of the 826 single microscopic phytoplanktons counted from the surface and bottom layers of water, 63.8% belonged to the Chlorophyta, 22.9% to the Bacillariophyta and the remaining 13.3% were Cyanophyta. The  Chlorophyta population was made up of seventeen (17) species belonging to seven (17) genera. Actinastrum, Pediastrum, Phacus and Phytoconia species were detected only in the bottom water whilst Ankistrodesmus, Coelastrum, Chlorella, Euglena, Microspora, Mougeota, Scenedesmus, Spirogyra, Straurastrum and Ulothrix were found in both layers. Spirogyra was the most predominant amongst the Chlorophyta in the surface water consisting 70.6% at this layer and 44.3% of the Chlorophyta population of the bottom water. Cyanophyta belonging to nine genera (Anabaena, Anacystis, Chroococcus, Gomphosphaeria, Lyngbya, Nodularia, Oscillatoria, Phormidium and Stignonema) were isolated in the water. Oscillatoria princeps was the most predominant Cyanophyta at the surface (36.1%) and bottom (52.6%) waters. Members of the Bacillariophyta found at the surface and bottom layers belonged to six (6) genera (Asterionella, Diatoma, Fragilaria, Melosira, Navicula, and Synedra). Members of the Cyanophyta which were isolated from the gut only were Merismopedia elegans, Oscillatoria tenius and Planktothrix agardhii. Practical implications of the findings are discussed.