1. Shell height frequencies of the fresh-water cockle, Corbicula elatior, sampled in the period of 1960 to 1963, are analyzed to assess the age composition and average growth pattern. Cumulative frequencies in a sample are traced on a probability scale, and the points of inflection on a probability graph are assumed to dissect age groups. 2. Seasonal growth of Corbicula elatior in the Naktong River ill as follows: Young cockles settle down on river-bed by June and grow rapidly during the summer season, reaching 14mm in shell height by October. From October to April the growth is very slow. The rapid growth in the second year starts around in May. 3. Survival rate per year for Corbicula elatior in the Naktong River is estimated to be $5~10\%$ by age composition.