| In the marine environment, the species with attachment habits such as algae, sponge, hydroids, barnacles, bryozoans, shellfish, sea squirts, often colonize the surface of ships, floating raft, net cage and other facilities. Therefore, these organisms are named as Marine Fouling Organisms.The harm caused by Marine Fouling Organisms can not be ignored. Especially in aquaculture, the marine fouling organisms will affect the normal growth of cultured species, and even result in a large number of their death, or also accelerate the aging of culture facilities.Thus it is necessary to carry extensive and in-depth reseatches.From Sep. 2006 to Aug. 2007, a study was conducted in Liu qing River Bay, Qingdao to examine the species composition and distribution of fouling organisms on scallop farming cages using test panels. A total of 65 species were identified, and the dominant species were Ulva lactuca, Enteromorpha linza, Polysiphonia urceolata, Crassostrea gigas, Mytilus galloprovincialis, Membranipora grandiella, Didemnum moseleyi. The main attachment period of the fouling organisms was from May to Nov. The monthly biomass reached a maximum (637.46 g/m2) in Sep., and the highest amount (3121.28g/m2) of the seasonal biomass appeared in autumn. Among semiannual panels, the second half year-panel had the maximum biomass which was 5924.57g/m2. The annual panel biomass was 3551.58 g/m2. The vertical distribution of the species indicated that the species were mainly algaes and amphipodas on the top panels, while compared with the bottom panels, the species were mainly various fouling animals such as bivalves, ascidians and so on. From the point of view of the species diversity, the species number in summer and autumn was larger than in winter and spring, and the community eveness was the lowest in auumn. We also discussed the effects of species interdependence, season and submersion period on the fouling organisms community, and preliminarily suggested the figure of the fouling organisms community succession for one year was that: following the microbial film phase, the fouling organisms community began to enter a medium-term phase, and then continued development. The community had experienced the successive emergence and disappearance of bivalves, algaes, amphipodas and hydras in this phase. Finally, on the annual panels a variety of fouling organisms pose a complex community in which the dominant species was Mytilus galloprovincialis, but it hadn't yet formed a stability community.Vitellogenin (VTG) is the precursor of vitellin (VT),and has been much attention. For oviparous animals,yolk formation and accumulation are the important events in the process of oogenesis. VT playing important biological functions is the major component of yolk in the eggs, and provide a great deal of nutrition for the development of oocytes and embryos. So the vitellin precursor VTG possesses high scientific value. It has been study widely and deeply in vertebrates, insects and crustaceans.However, in molluscs, the related researchs are inadequate, especially about the source of vitellogenin, the controversy still exists. In the present study, an important commercial species of aquatic, Zhikong scallop Chlamys farreri was selected as the research object.We cloned full-length cDNA of Cf-vtg from Chlamys farreri using homologous cloning strategy and rapid amplification of cDNA end (RACE) technology. At the same time the spatio-temporal expression of Cf-vtg transcripts was analysed by RT-PCR and in situ hybridization, and the expression site of Cf-vtg transcripts was identified in the adult individual. Finally, we also conducted a preliminary research on the expression induction of Cf-vtg by in vitro estrogen.Cf-vtg cDNA consisted of 7604 nucleotides. The open reading frame(ORF) encoded 2296 amino acid residues, with a putative processing site, R-X-K/R-R, recognized by subtilisin-like endoproteases. The deduced primary structure of putative vitellogenin in Chlamys farreri was 89% identical to the vitellogenin of Patinopecten yessoensis, and shown similarity to vitellogenins of various other mollusc, fish, crustacean and nematode species, especially in the N-terminal region.Semi-quantitative RT-PCR showed that Cf-vtg mRNA was expressed mainly in the ovary, with weak expression in the hepatopancreas, and no expression in testis and other organizations. The Cf-vtg gene expression decreased gradually with the ovary maturation. In situ hybridization analysis further localized Cf-vtg mRNA to the follicle cells surrounding the oocytes in the ovary, but not in the hepatopancreas. We concluded that the follicle cells are the site of Cf-VTG synthesis in Chlamys farreri. Detecting the expression of Cf-vtg in the hepatopancreas RT-PCR might be caused by mixing with a small portion of the ovary during the process of sampling in the hepatopancreas.The researchers injected 17β-estradiol into the gonad of female individuals to induce Cf-vtg gene expression. Semi-quantitative RT-PCR analysis revealed that Cf-vtg gene expression was significantly enhanced in the ovary of the individual experiencing the injection. It was concluded that 17β-estradiol could promote the synthesis of Cf-VTG. |
PDF Full Text Request