Reared Spring Spats The reared spring spats fertilized on April 19, 1972 grew to commereial sizes in August the next year with a shell length averaging 70 mm and a body weight 27.1 g.The growth of shell length was faster in the first year than in the second year. The increase of shell length reached as high as 0.358mm per day and the maximum daily growth rate was 6.3%. The inerease in shell weight was also greater in the first year than in the second but its rate. however. was smaller Generally speaking, the second year ean still be regarded as blooming period for the growth of mussels. In the winter of the first year when the temperature was very low, the shell part virtually ceased to grow while the soft part continued to inerease in weight.In the spring of the next year (from April to July) as a result of breeding the soft part undergone several times of monthly cyclical weight reduction, the aggregate loss of weight often amounted to 1.2 times the weight of the soft part itself. The greatest reduction in weight (60%)was recorded during breeding period from late April to early May. Reared Autumn Spats The reared autumn spats fertilized on October 5,1972 grew to an average shell length of about 10 mm in June the next year which were then available for produetion purpose. Natural Spring Spats In the last ten days of August, the average shell length of natural spring spats was about 10 mm(the bigger ones measured 26 mm)and were good for attachment in flowing water. In mid-september, many individuals grew to a shell length of 15 to 25 mm(the bigger ones reached 36 mm), which were good for reattachment by binding them to new ropes with netting. The natural spring spats attached to the wharves of Yantai port and those growin on the reefs were much smaller in size than those on the cultured rafts. As to those spats growing on the cultured rafts at Jingou Bay, those nearer the site from the seashore were bigger in size than those at the farther site.