The reproductive cycle of white clam Spisula solida (L.) (Mollusca: Bivalvia): Implications for aquaculture and wild stock management

The dynamics of the white clam's (Spisula solida) reproductive cycle along with its nutrient storage and exploitation strategy in the Algarve coast (Portugal) was studied throughout the year 2003. The timing of gametogenic development and spawning of S. solida were analysed through histological preparation using qualitative and quantitative criteria. Condition index and biochemical composition were determined in order to provide information on energy storage and utilization. Seawater temperature is a primary environmental factor determining reproductive development and spawning of S. solida; reproductive activity occurred during low temperatures. The spawning period began in late winter as a consequent response to the increase in seawater temperature and extended through spring. During this period, the condition index and the gonadal index decreased. In June, most of the population was spent and big resting oocytes appear dispersed in the gonad. In summer, the specimens were found to be in the resting phase and condition index increased to its maximum value as a consequence of reserves storage. Gametogenic activity was initiated coincident with decreasing temperature in September, but a sudden increase of this environmental parameter in October disturbed the gametogenic process and a second spawning occurred. In this period, the synchronism between males and females of the population was lost. The striking consumption of glycogen reserves developed during the previous August and consequent biosynthesis of lipids during gamete formation occurred. In the following two months, reproductive synchronism was restored, and storage of reserves and gametogenesis took place concurrently. In December the entire population was in the ripe stage of gonadal development. Moreover than a consequence of gametogenesis during autumn/winter, lipid behaviour reflected the energy accumulation process and its conversion to somatic development in spring/summer. The reproductive strategy adopted by S. solida makes possible broodstock manipulation in terms of conditioning in aquaculture. The information obtained in this study is important for assessing sustainable management of wild stocks as well as for estimating its potential for aquaculture production.