In 1975 we conducted an experiment on rearing of mussel spats in late autumn byraising wster temperature in a concrete tank measuring 10M. in size half-buried in theground. The results revealed that the maximum output of each tank reached to 1.8×10⁷pcs./10M⁸ and the average output of all the four tanks used was 1.2×10⁷pcs./10M⁸Itreached to the record of the high-yield tank in the spring of 1973, and the averageoutput record in the spring of 1975. In rearing of autumn spats water temperature should not be lower than 10℃ inorder to ensure the larvae have a steady rate of growth and successfully go through themetamorphosis. If the water temperature was kept over 13℃, the growth rate would beaccelerated. Larvae could live normally and actively at the water temperature above 8℃.While below 7℃ or 5℃, the larvae lay down to the bottom of the tank under a certainperiod of time and their growth was virtually stopped and the process of metamorphosiswas also retarded and a large number even died. As soon as the water temperature was restored to 9℃ or higher, they could onceagain resume their normal activities and continue to grow. After the completion of metamorphosis, the spats possess the adaptability to the change of water temperatures. If the water temperature was gradually lowered from16℃ to 2.8℃ by one degree a day, the young spats were able to withstand and adaptthemselves to this rate of change. Thus, it was made possible to transfer the culturedspats in winter to sea areas where they were left to pass through the cold season. At 0℃ or thereabouts, the young spats ceased to grow but they were able to survivethroughout the winter. Based on the above temperature requirements, the installment of an additionalsmall water-heating equipment is now in use in the spat rearing room and the problemsof production in winter can be readily solved. With such an installation, an ordinaryrearing room can maintain all-year-round production of spats, that is. can cultivate 4crops of spats in a year two crops in spring and two in autumn.