Ring formation and annual growth in Corbicula consobrina Caillaud, 1827 (Bivalvia, Corbiculidae)

Abstract

The growth of C. consobrina of the White Nile near Khartoum was studied during March-December, 1977 from material collected from fish guts every two months. It was found that the growth season extends from February to July in correlation with the rise in temperature. Food was abundant and the concentration of the dissolved calcium in the river water was also increasing. During the flood season from July to October, the clams entered a resting state as a result of the annual siltation and consequently growth was arrested. Growth rings were found to be formed as a result of the siltation-induced resting state. There is evidence that little growth occurred during the cooler months from October to December. The development of the false rings on the shells is possibly a result of the changes in the water levels. Analysis of the growth of the adult clams showed that there is a clear size-time relation; there was close agreement between the calculated maximum sizes and the actual data collected from the field. Other examples from Sudanese inland waters were also discussed. The role of the annual hydrological cycles in regulating the populations activities and hence the growth of the individuals was found to be important