The oysters (~8-10 cm in shell length) were exposured in 0.1 % of colchicine solution for 12 hrs. The oyster meat was removed from shell and the gills were cutted off. The gill tissue was prepared by cutting into small pieces and mince gently before transferred into a centrifuge tube contained with 8 ml of 0.075 % KCl hypotonic solution. The samples were treated in the solution for 30-40 min prior to centrifuge at 1,500 rpm for 8 min. The supernatant was siphoned out and the remaining sediment gill tissue was fixed by 8 ml in freshly solution (methanol: acetic acid; ratio 3: 1). The sample was then taken to centrifuge for 3-4 time until sediment cell was cleared. The sediment cell was dropped on a clean and warm slides and air-drying (Wang et al. 2004, Khrueanet et al. 2013)