Triploid shellfish are useful for aquaculture because of their sterility,superior growth and improved meat quality.Tetraploid are also valuable for 100% producing triploids through mating with diploid.We tested polyploid induction in Japanese scallop,Patinopecten yessoensis,by inhibiting polar body Ⅰ (PB group) and both polar bodyⅠandⅡ (PPB group) in newly fertilized eggs.Cytochalasin B (0.6 mg/L) was applied at 11～22 min post fertilization (PF),and terminated in PB group when polar body Ⅰ was released about 70% in untreated eggs,in PPB group when polar lobe was observed in control group.The treatment and its control were repeated 5～7 times using different pairs of parents.The ploidy was determined by counting chromosome number at embryo stage,and then was detected by flow cytometry (FCM) at larvae stage and juvenile stage.\;In PB group,aneuploid (31.13%),triploid (3.96%),tetraploid (17.46%) and pentaploid (46.65%) embryos were produced,and in PPB groups,pentaploid embryos became higher (56.2%),triploid and tetraploid were 2.42% and 9.11%.At day 3 PF,the larvae showed tetraploid,pentaploid and aneuploid peaks through checking with FCM in PB group,and showed mainly higher pentaploidy peak in PPB groups.However,at day 14 PF diploids were mainly left,sometimes with small triploid peak.It suggested that most tetraploid,aneuploid and pentaploid larvae were died within the first two weeks PF.At three months PF,a few diploid juveniles were harvested in three control groups.Only 12 juvenile scallops were harvested in one of treated group (PB-7),and 11 of them died accidentally,the alive one in treated group was triploid through checking with FCM.
