Age determination and growth rate of a Callista chione population from the southwestern coast of Portugal

The age and growth of the smooth clam Callista chione from the southwestern coast of Portugal were estimated during a 1 yr study period by using both the surface growth rings and internal shell microgrowth lines (by acetate peel method). The von Bertalanffy growth curves obtained by these 2 methods were, respectively: Lt = 91.9(1 - e - 0.18 (t + 0.22) ) and Lt = 98.1(1 - e - 0.15 (t + 0.43) ). Based on these, the counting of surface growth rings is appropriate for a quick age estimation of individuals up to 10 yr old (~75 mm shell length, SL). For older specimens, analysis of the growth lines in the cross section of shells is recommended, because close to the shell border it becomes difficult to distinguish growth rings on the shell surface. Rapid shell growth occurred in spring and summer, whereas slow growth occurred during autumn and winter, with the deposition of an annual growth ring. The over- all growth performance and the phi-prime index were used to compare growth parameters with data from literature about venerid bivalves. These parameters indicated that Callista spp. have a higher growth performance than other venerid bivalves and this is correlated with geographical latitude. The smooth clam achieves sexual maturation at 4 yr of age and reaches the minimum landing size (60 mm SL) after 5 yr.