| The scallop, Chlamys farreri, is used to be one of the major species cultured in North China. However, the great expansion and intensification have induced the occurrence of disease since 1997 which cause apparent stagnation to the development of the scallop industry. The disease has been becoming epizootics in Shandong and Liaoning provinces from then on. Epidemiological and pathological study shows that the pathogen of the massive death of the scallop was acute viral necrobiotic virus (AVNV). The seasonal character of the pathogeny and the target organ which was infected is now clear. A number of pathogen detection technologies are established including FQ-PCR assay which is a powerful tool for the detection of AVNV with rapidity, sensitivity, specificity, accuracy and quantification. This establish a foundation for further research on AVNV, such as pathogenic mechanism of AVNV infection, epidemic spread process of pathogenic, and so on. The scallop is a kind of filter-feeding shellfish which can only intake of-a certain size of plankton in the sea waters. In order to make sure the possibility of AVNV infecting scallop by eating plankton, this study apply FQ-PCR detecting technology to quantify AVNV carried by plankton in some months in two Shellfish Culture Areas. The purpose is to clarify the seasonal changes of plankton carrying AVNV. So that we can know the epidemic spreading character of AVNV and provide a theoretical basis for prevention and control measures.In order to clarify the relationship between the plankton and transmission of AVNV, and to afford proof for tracing transmission track, the sea water samples were fetched from 50cm and 300cm depth in the sea area for culturing Chlamys farreri at Shazikou of Qingdao and Sanggouwan of Rongcheng regularly from May to November in 2009, and the plankton was collected by 25μm,3μm,0.22μm pore size filter, respectively. The AVNV carried by the plankton was identified by FQ-PCR. The results showed that the virus could be carried by the plankton, and the virus number in the plankton from both sea area arrived the peak in August, the highest number of AVNV identified for the samples from Shazikou sea area was 8.21×106copies per litre sea water, and that was 2.98×105copies for the samples from Sanggouwan sea area. Based on the number of AVNV carried, the plankton group with different particle size was 3μm-0.22μm,25μm-3μm and>25μm from high to low in turn. The number of AVNV carried by the plankton from 50cm and 300cm depth was not different significantly. This is the first report about AVNV carried by the plankton from the sea area for cultured scallop, which indicated that the plankton could carry AVNV, and the number of AVNV carried by the plankton was dissimilar with the plankton particle size and with the plankton collected seasonally. These implied that the scallop could be infected by taking the plankton carried AVNV as food, and the plankton was crucial infector of AVNV.In order to illuminate about the function of macroalgae on transmission of AVNV, samples of macroalgae were collected randomly from sea area of Shazikou of Qingdao and Sanggouwan of Rongcheng in 2008 and 2009. The AVNV carried by different species of macroalgae was identified by PCR and FQ-PCR technique. Twenty of 36 macroalgae samples collected at the sea area of Shazikou in 14 months were AVNV positive, accounting for 55.56%, the positive samples belong to seven species including U.pertusa, E. prolifera,G. crinale, E. Linza, H.floresia, G. textorii, Cladophora, and 5 of 24 macroalgae samples collected at the sea area of Sanggouwan in 9 months were AVNV positive, accounting for 20.83%,the positive samples belong to three species including U. pertusa, H. floresia, Sargassum. U. pertusa is main macroalgae carrying AVNV,11 of 12 U. pertusa samples collected at sea area of Shazikou were AVNV positive, the highest AVNV number was 7.68×104/0.1g in fresh sample collected at August 25,2009, while at that of Sanggouwan,3 of 5 U. pertusa samples collected were AVNV positive, the highest AVNV number was 3.06 ×103/0.1g in fresh sample collected at July 2009. The present results implied that plankton and some of macroalgaes could carry AVNV, which the scallop culturing could be infected by taking plankton carrying virus as food. The role of macroalgae carrying AVNV in transmission of AVNV remains to be further studied. AVNV (Acute Viral Necrosis Virus) is the pathogen led to masse mortality of cultured Chlamys farreri, but the transmission of the virus is unknown.We used 9 cultured microalgae species as control to analyze the species diversity of eukaryotic planktons in waters of scallop cultivation. The 18S rRNA genes (VI to V3 region) of 9 months eukaryotic planktons in waters of scallop cultivation of Shazikou were amplified by two universal primers (Euk516r-GC and EuklA). These amplified DNA fragments were analyzed by parallel DGGE. The result indicated that the length of amplified fragment is approximately 560 bp. The primer sets gave a single band and separated in different position when used with nine cultured microalgae species. Diversity of eukaryotic plankton assemblages of 9 months plankton assemblages at culture area for scallop witch is 2 meters deep was analyzed by DGGE. The results showed that the number of different electrophoric bands was 38, of which 3 bands existed in all nine months, taking 7.69 percent of total bands number, and there were 11 characteristic bands in all, taking 28.2 percent. There were markly various fingerprints in different months, Shannon index is 0.4632. Similarity analysis shows that March and April 2009, May and June 2008, as well as October and December 2008 have similar eukaryotic species respectively. UPGMA clustering analysis based on different eukaryotic plankton assemblages shows that May, June and August 2008 were grouped into a cluster, January, February, March, April 2009 into the other cluster, which implied that similarity of the eukaryotic plankton species between close month was high. |
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