Abstract:The pen shell, Atrina pectinata, has high commercial and scientific research value because of the lack of large-scale culture in China. In recent decades, many problems such as overfishing, deterioration of marine eco-environment, and failure of artificial seedling breeding, have drastically reduced the amount of wild sources. However, there are few reports on A. pectinata systematic classification and no karyotype reports until now. To explore the cytogenetical characters and identify the status of germplasm resources of A. pectinata in northern China, by adjusting the water temperature of temporary rearing, and using the healing hyperplasia tissue of gills for chromosomal investigation, we improved the methods of chromosome preparation, and obtained many well-spread mitotic chromosomal plates of seven male and five female A. pectinata. The results revealed that a certain degree of temperature-change stress during temporary rearing could promote the proliferation of somatic cells effectively in the short term; gill-healing hyperplastic tissue has mass proliferation of cells in mitotic metaphase. The karyotypes of both sexes were examined separately. A. pectinate has 17 pairs of chromosomes (i.e. n=17, and 2n=34); there were obvious differences in karyotype between males and females; male karyotype formula is 2n=8m+10sm+16st；female karyotype formula is 2n=6m+10sm+18st. The first pair of the particularly larger chromosomes were heterotypic in male somatic cells; the No.14 pair of chromosomes was metacentric in males but telocentric in female metaphase somatic cells; the primary sex-determination mechanism is XX/XY type. The newly improved methods for chromosome preparation could be beneficial to large-scale shellfish germplasm identification and classification.
