| Crassostrea hongkongensis mainly distributing along the coast of the Guangxi and Guangdong province. It is popular for its fleshy meat and delicious taste. So, its market price is much higher than other kinds of oysters. Nowdays, Crassostrea hongkongensis is large-scale cultivated. And it becomes the most important economics oyster breeding pecies in the south of China. However, the quantity and quality of Crassostrea hongkongensis's simi-artificial spat collection is not stable, which makes it still unable to meet the market demand. In addition, loss of strictly genetic variability and seedling quality degeneration has become the main obstacles to the development of oyster industry. So, genetic improvements are needed to surmount the obstacles and to breed excellent species. In the study, we used the Crassostrea hongkongensis as the experimental material to discusses the indoor artificial seedling technology, and researched the complete diallel cross experiment with two different geographic population of Crassostrea hongkongensis, then evaluated the effect of crossbreeding. The results will accelerate the development of Crassostrea hongkongensis industry. The main results are as follow:1?The research of artificial breeding technologyIn this paper, a preliminary study of indoor artificial breeding of the Crassostrea hongkongensis was carried out. We compared the impacts of breeding density and algae types on larval phenotypic traits and analyzed the effects of four settlement substrate. Results showed that the larvae growth, survival, metamorphic rate decreased with the increase of breeding density, which can occur the delay metamorphosis phenomena; The best breeding density range of umbo period is 5-10ind./ml. For the initial feed, both Nannochloropsis sp and Isochiysis Zhanjiangensis are excellent to the Crassostrea hongkongensis larva. But with the growth of the balanced demand, the mix feeding was better than single fed groups. During metamorphic period, the oyster shell was the best choice, followed by scallop shell and polyethylene corrugated plate, and pat of cement was the worst. This study provides the foundational theory of reproduction biology on Crassostrea hongkongensis, and also supplies the practical experiences for indoor artificial breeding.2?The Salinity influence on fertilization and hatching, growth and survival of larvae and juvenile in Crassostrea hongkongensis hybrid of two groupsThe study of the salinity influence on fertilization and hatching, growth and survival of larvae and juvenile in Crassostrea hongkongensis hybrid of two groups has been carried out in the indoor controlled conditions. The results show that in five different salinity conditions, the best salinity range of the selfing group Maowei Sea(MM) and Zhuhai (ZZ) both are 15-20‰, the fertilization rate reached more than 85%. While at the salinity 20‰, the fertilization rate is highest of all the groups. The optimum salinity range of hatching is 15-25‰, while at the salinity 20%o, the hatching rate is highest and the aberration rate low. At the larva stage, the hybrid grow fastest when the salinity is 15‰. And when the salinity at 15-20%o, the larva survival rate is higher than the other salinity. But the larvae could not complete metamorphosis in salinity 10‰. Juvenile stage suitable salinity was 15-25‰, the best growth and survival salinity was still 15‰. The salinity 25‰?30‰ groups recovery growth normally while inhibited growth at the early stage. The study shows Crassostrea hongkongensis can have very strong adaptive capacity.at both high salinity and low salinity conditions.3?Study on diallel cross of Crassostrea hongkongensis from two geographical populationsTo evaluate early heterosis of Hong Kong oyster Crassostrea hongkongensis between two geographical populations (Z:Zhuhai, M: Maowei Sea), the 2×2 diallel crosses was conducted, which including two self-fertilized groups (MM, ZZ) and two reciprocal crosses (MZ, ZM). Results showed that there was no growth heterosis before 9 days, but the positive heterosis was observed on 12 days for MZ group with survival heterosis. However, the positive heterosis of growth and survival ability appeared for ZM group during the plantonic stage. At spat stage, the positive growth and survival heterosis was 7.86±3.12,17.47±13.14 for MZ group, and 8.33±1.41,2.86±1.08 for ZM group, respectively. Above results indicates that heterosis can produce in different populations, and it will provide theory and practice of utilization for heterosis of Hong Kong oyster. |
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