With a view to developing mussel culture and to supply shandong seashore with more spats, we launched in 1972 and continued a research program in 1973. After careful investigation, it has been confirmed that Yantai is .an ideal site for seed-bed. Mussels along the coast of Yantai are found to have two fattening periods and two thinning periods. The fattening period is in September， and in December to April of the next year. During this period the fatness of the mussels which is calculated as the weight of dried meats/the weight of shells, will increase by more than 20%.The thinning period during which the fatness of the mussels will decrease to less than 15% is in early May and in June to August.