The age of clam can be determined by light penetration method.When a common light penetrates the shell of clam|the stiped pattern on the shellappears clearly. The bright and dark portions of the stripes are formed respectivelyfrom May to October and from October to Mae of the next year. The time of forma-tion of dark and bright portion is very definite among all of the age groups. There-fore|the absolute age of clams can be datermined by the bright-dark boundary onthe shell or clam.