| Flat oyster (Ostrea denselamellosa Lischke), which classied to Ostrea, usually lives in the subtidal zones along the north and south coasts of China, as well as the Korean Peninsula and Japan. The flat oysters'softbody is not only rich in taurine, vitamin, highly-unsaturated fatty acids, but also has low fat, low cholesterol, and inorganic salts. However, because of the flat oysters' scattered distribution in Chinese coastal areas and less resources, and other reasons, their economic value has not been developed and utilized. In recent years, habitat destruction and deterioration of marine severe population declines. Thus, it is necessary to establish the techniques of artificial reproduction of the flat oysters, O. denselamellosa, for the protection of natural resouces and initiating aquaculture activities in this species.The preliminary study was conducted about the external shape, internal structure, and other physiological functions of different phases of flat oyster by using HE staining slicing techniques, the observation of larvae and photomicrography techniques. And other studies was conducted, for instance, the artificial reproduction, the effect of environmental factors, i.e. the salinity, the temperature,the density and the different dietary, on the growth and survival of larvae and spat. The main research results are as follows:1. This study is the first report of the microscopic features of larvae and gonads of O. denselamellosa collected in Qingdao, China. Female oysters brooded larvae at the early veliger stage (130-140μm) in the infrabranchial chamber. Larvae in this chamber displayed a well-developed velum covered with long and short cilia; the adductor muscle was incompletely developed. The digestive system of the larvae, including the mouth, esophagus, stomach, digestive gland, and intestine, was identifiable in histologic preparations, indicating that the veliger larvae in the brood chamber were capable of feeding using the velum and cilia. Diameters of ripe eggs in the ovary ranged from 80-90 2μm. Most female oysters collected in June 2009 were spawning or absorbing whereas most of male oysters were spent or sexually inactive. The eye point and foot are the sign of settlement of flat oyster larvae and disappear after metamorphosis.2. The broodstock culture and larvae rearing were investigated in the oyster O. denselamellosa for the first time. The effects of salinity, water temperature, densities and diets on growth and survival rates of the larvae of O. denselamellosa were also examined. After larval rearing of about 28 days, the larvae developed to the stage of metamorphosis characterized by the appearance of eye spot at the temperature 23-25℃and salinity 28-30. As the temperature varied from 24℃to 32℃, the growth rate of the larvae was positively correlated to temperature, but the survival rate negatively correlated to temperature. For the four experimental groups with stocking densities of 1,2,3 and 4 larvae ml-1, larvae reared at the lowest density had the largest mean size, but there is no significant difference in survival rate. Compared with two monoalgal diets of Isochrysis zhanjiangensis and Platymonas subcordiformis and a mixed diet of I. zhanjiangensis and Chlorella vulgaris, the highest growth rate was achieved with the mixed diet of I. zhanjiangensis and P. subcordiformis. The setting rates of the oyster larvae varied depending on the type of substrate used. The scallop shell had the highest setting rate of larvae, followed by plastic sheet, screen mesh, monofilament nylon and plastic film.3. The effects of reduced salinity on O. denselamellosa spat were studied at 24-26℃(natural temperature),28℃, and 31℃. Growth and survival rate were studied at salinities of 32,30,26,22 and 18 for a period of 30 days. In the period of cultivation of flat oyster spat, the growth rate became higher as the water temperature increased, and the appropriate temperature for growth is 24-29℃. The effect of salinity on the larvae and spat of flat oyster shows that at different developmental stages of the flat oyster, the salinity tolerance is different, for example, larvae has narrower temperature tolerance than spat.The reason of the different temperature tolerance between larvae and spat maybe lead by the different environment of their respective life, stable for larva but changeful for spat. |
