| There are rich shellfish resources such as big razor clam and Atrina pectinata under the shallow sea in Rizhao area. The output of big razor clam reached 1300 t in 2002, while that of A. pectinata was 342 t in 2005. But the resources have decreased markedly in recent years due to overfishing. Through taking artificial enhancement measure such as juvenile releasing, the resource of big razor clam started to rise again from 2004. The result of sampling investigation from September to October in 2008 showed that the amount of economical shellfish resource became smaller in intertidal zone with the mean biomass was only 24.3 g/m2. The minimum biomass was 6.3 g/m2 in Wangjiazao area, and the maximum was 40.4 g/m2in liujiawan area where the populations are protected well.A culture experiment was carried out in Taoluo area from April 2007 to May 2008 in which four kinds of shellfish were cultivated in an intertidal region of 20 hm2. About 164.8 tons of juviniles were cultured in the cultivated area. The output of adult mollusks reached 755 tons during the period, the mean output was 2500 kg per Chinese acre, the actual net income was 962000 yuan and the mean net income was 3200 yuan per Chinese acre. The dynamics of growth with the seasonal variation were consistent among the four kinds of shellfish, which was quick during May to July, slow during August to September, and stopped growing after November. There was an obvious exponent relation between shell length and body weight, the body weight was extremely relevant to the shell length.The raft culture of shellfish in shallow sea started from early 1980s in Rizhao, the main culture species were Mytilus edulis and Chlamys farreri. Its development has experienced three stages, in the first stage M. edulis was the only cultivated species, in the second stage C. farreri was cultivated in raft culture and developed quickly, in the third stage the M. edulis cultivation started to occupy the dominant position again and the C. farreri cultivation began to recover gradually. In order to explore the new cultivation technology of C. farreri, an experiment was carried out in which 5 million grains of C. farreri juvinil and 5 million grains of hybrid scallop juvinil were purchased to culture in Rizhao from Shidao in November 2006. The result showed that the SGR in shell length of hybrid scallop ranged from 0.12%/d to 1.15%/d, which was 0.11%/d to 1.10%/d for C. farreri, the SGR in body weight of hybrid scallop ranged from 0.22%/d to 2.76%/d, which was 0.23%/d to 2.84%/d for C. farreri, there seemed no difference in the SGR of the two kinds of scallops, though the SGR in body weight was obviously higher than that in shell length. The changes of SGR in every growth parameter along with water temperature were basically the same for the two kinds of scallops. From November to February, the growth rate dropped to the bottom with the decline of water temperature, but the first peak of growth occurred from March to July along with the rise of water temperature. From July to August its growth rate postponed and reached the second bottom of the year with the further rising of water temperature, but the second growth peek occurred from September to October with the water temperature dropped to 20℃about. After finishing the experiment, the measurements of the samples showed that there were no obvious differences between the average shell height and body weight of the two kinds of scallops (p≥0.05), but there was an obvious difference of the survival rate between them(p≤0.01), the survival rate of C.farreri was 65%, the average weight of one cage was 5.35kg and average output was 2140kg per Chinese acre, whereas the survival rate of hybrid scallop was 90.1%, the average weight of one cage was 7.75kg, average output was 3100kg per Chinese acre. So the total output for hybrid scallop increased 44.9% than C. farreri.Based on the fact that DNA methylation is related with gene expression regulating, methylation sensitive amplified polymorphism (MSAP) was used to analyze the difference of methylation status between them. With 12 primer combinations,567 amplified loci were identified. In C. farreri 211 eytosine loci (about 37.21%) were polymorphism methylated including 71.56% hemi methylated and 28.44% fully methylated. In hybrids 208 eytosine loci (about 36.68%) were polymorphism methylated including 71.63% hemi methylated and 28.37% fully methylated. As a whole, the number of eytosine methylation loci was not significantly different among C. farreri and hybrids (p≥0.05) suggesting that some loci were methylated while some loci were free-methylation. However, the methylated status in a few of single site was different between C. farreri and hybrids implying that the expression of some genes might be different between C. farreri and hybrid and these changes may be related to disease-resistent phenotype that appeared in hybrids. |
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