Seasonal variation in growth and gonadal development of the Pacific oyster “Haida No. 3” in relation to the nutritive components

To elucidate the growth characteristics and reproductive strategy of the Pacific oyster Crassostrea gigas “Haida No. 3”, the relationship between environmental factors and seasonal growth variations, gonadal development, the general nutrient components of the mantle, gonadal-visceral mass, gill and adductor muscle were examined from November 2016 to October 2017. Results indicated that in winter (from January to February), the growth of C. gigas “Haida No. 3” was slow and its gonad was in the resting stage. With the increase in water temperature (from March to April), gametogenesis began and the gonads of both sexes developed synchronously. The high growth rate of shell and the significant increase of wet weight were observed from April to May. During summer, the growth rate of shell declined along with gamete development. In July, C. gigas “Haida No. 3” lost weight due to gametes emissions. In autumn, the shell height and wet weight increased significantly. The biochemical analyses showed glycogen content of all tissues decreased significantly during sexual maturation, whereas the protein and lipid content in gonadal increased as the gametes matured. It indicated that carbohydrates provide energy for gamete development, lipids and proteins are major structural substances of gametes. During the autumn, protein was rich in the four tissues and provides the material basis for the rapid growth. Moreover, the major function of mantle is to secrete shell, its significant increases in glycogen and lipid content from August to September indicating that the rapid growth of the body requires a certain amount of energy reserve. The present study demonstrated that the growth and reproduction activities of C. gigas “Haida No. 3” are affected by seasonal changes in seawater temperature and are closely related to the nutrient composition of tissues. Organism experience the rapid growth period in spring and autumn, while summer is the spawning season. Glycogen is the main source of energy for growth and reproduction, lipids are the major structural substances of gametes, and protein is the material basis of rapid growth.