Abstract:Triploid of Crassostrea hongkongensis was induced by blocking the second polar body release by cytochalasin B(CB) and 6-dimethylaminopurine (6-DMAP), and we compared the two methods in the aspects of triploid rate, cleavage rate, velar larvae gain, cost and so on. The effects of the concentration of CB or 6-DMAP, induced occasion, induced duration and zygote density on inducing triploid C. hongkongensis were also discussed. The results showed that:when oyster zygotes were fertilized at 28-30℃ and salinity at 15-25, and dealt with 0.50 mg/L CB began at 15-18 min, post fertilization lasted 20 min, and incubated density of zygote when treatment was about 2.0×108 ind/L. These were optimum conditions under which triploid of C. hongkongensis was induced by CB. In this case, triploid yield was 100%, cleavage rate was 53.16%-63.00%, velar larvae gain was 47.32%-53.09%, the efficiency of triploid induction was 0.47-0.53, and the cost was 260 RMB/L. The surrounding when fertilization, and induced occasion was the same as those in CB, but oyster zygotes were dealt with 75-100 mg/L 6-DMAP last 20-25 min, and incubated density of zygote when treatment was about 4.5×107 ind/L. These were optimum conditions of triploid of C. hongkongensis was induced by 6-DMAP. In this case, triploid yield was 62.52%-72.36%, cleavage rate was 60.00%-66.25%, velar larvae gain was 74.43%-90.00%, the efficiency of triploid induction was 0.47-0.65, and the cost was 139-185 RMB/L. Through comprehensive comparison between CB and 6-DMAP, we could draw the conclusion that 6-DMAP was more applicable in triploid production of C. hongkongensis than CB. This study provided the basic theory and practical experience for polyploidy breeding in oyster.