Gametogenic development and spawning of the mud clam, Polymesoda erosa (Solander, 1876) at Chorao Island, Goa

Abstract

The reproductive cycle of Polymesoda erosa was studied over a 12 - month period from July 2004 to July 2005 at Chorao Island, Goa, India. Macroscopic observation revealed that Polymesoda erosa is dioecious and gametogenic development was synchronous between the sexes. Sexes can be determined at a total length of less than 34 mm, based on the colour of the gonads. The gonadosomatic index (GSI) indicated that gametogenesis began in November and by March-April most clams were ripe. Spawning began in August and by October nearly all clams were completely spent. Maturation and high GSI were observed to begin during the warm summer months with low GSI values in August (20.0) and September (22.0). Correlation between GSI and chlorophyll a content in the adjacent estuarine water suggests that gametogenesis in mud clam is directly related to the phytoplankton production. The condition index (CI), which is generally used to characterize the physiological activity of organisms, varied from 1.9 in September to 4.7 in March, with low values during the spawning period. The clams attained their best condition in quality of flesh weight during March-May. The data presented here should provide valuable information on the timing of spawning events for P. erosa, necessary for developing sustainable management strategies and broodstock selection, which is crucial in aquaculture development.