Effects of ionizing irradiation of γ ray on mortality and growth of one year-old Pacific oysters （Crassotrea gigas） were studied. Irradiation was conducted at 4 ℃ and without sea water, and the survival, shell length, shell width, whole wet weight and condition index of irradiated oysters were measured. A biphasic dose response effect of γ irradiation on Pacific oyster with high stimulatory response dose range to 100 Gy, and strong hormesis effects had been observed. Gamma ray induced mortality happened within 90 days after irradiation, and the relation between dosage （D） and mortality at 90 days could be described by the equation of M90=0.0041D2-0.1816D （R2=0.9958） with an LD50/90 of 135 Gy, indicating that the Pacific oyster has strong resistance to γ irradiation. Growth in shell length, shell width and whole wet weight of Pacific oyster were also enhanced by 60 Gy of γ ray. The condition index was also enhanced by γ irradiation in the dosage range from 40 to 100 Gy, with the maximum stimulatory response of 2.5 fold of control value at the 40 Gy dosage, suggesting that the accelerating effects of γ ray on growth of the Pacific oyster led to increase in dry meat. Results of this study showed that ionizing irradiation might be useful in the improvement of production traits in shellfish.
Hybrid family of Argopecten irradians irradians was created by fertilization between two northern bay scallop individuals.Two families were analyzed in this study.The first family,Pa-Pb,is a pair mating between two scallops named Pa and Pb,while the second one crossed by individuals of Y1 and P0.Marker inheritance and segregation were studied in the 10 progenies of each family by randomly amplified polymorphic DNA（RAPD） analysis.102 RAPD primers were first screened by parental animals of both families.Only the primers with polymorphisms between the two parental animals in each family were selected for further analysis.In both families,parents and 10 progeny were analyzed with selected primers.In family Pa-Pb,a total of 122 bands generated from 12 selected primers.37 of them were polymorphic between two parents.The maternal Pa of this family had 17 molecular markers while paternal Pb had 20 markers.In Y1-P0,95 bands were produced by 10 selected primers.32 bands were polymorphic between maternal Y1 and paternal P0,who had 17 and 15 molecular markers respectively.In both families,each progeny analyzed in this study had at least 8 maternal markers and 5 paternal markers.Based on segregation patterns at all markers analyzed,we concluded that none of the progeny analyzed were from self-fertilization,and one-way hybridization between two individuals was successful in both of the two bay scallop families.
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.
