Studies On Cultavition And Chromosome Sets Stability Of The Mated Triploid Pacific Oysters, Crassostrea Gigas

The feasibility to produce triploid Pacific oysters Crassostrea gigas is studied in this paper by methods of cytogenetics and experimental biology. The chromosome composition and stability in mated triploid oysters are also discussed. The comparison of the biology characters between triploids and diploids is observed. This study is expected to be able to offer basic data to polyploid culture in Pacific oysters.I .Production of triploid by mating tetraploids with diploidsAll-triploid Pacific oyster seeds were produced in a large scale by mating tetraploid males, which came from American with the local diploid females. The mean fertilization rate was 48.27% for the cross group and 80.53% for the control group. The lower fertilization in the crosses may due to the deficiency in amount and the poor vigor of the sperm from the 4n males. Hatching rate, larvae survival and metamorphosis of eyed-larvae averaged 81.10%, 42.3% and 1.82% respectively in the cross groups, compared to 79.96%, 37.0% and 1.80% respectively in the control groups. A total 12 million spats were obtained in the cross groups. The crossed larvae were larger than that of the control and showed the superiority in growth. Results of analysis by flow cytometer at different stages showed 100% triploidy in the cross groups.II. The change of triploidy in mated triploid oysters during the cultureThe ploidy of mated triploid in period of lavae, spat, juvenile (3months), 1 year, 1.5 years and 2 years was detected by flow cytometer. The ploidy of mated triploid in period of lavae, spat, juvenile (3months) and 1 year was all triploidy (100%), but with the development and maturation, differentiation in ploidy gradually happened. In later detections, both diploids and 2n/3n mosaics were found in mated triploid oysters, and the proportion of diploids and mosaics got higher and higher with culturing. The triploidy reduced to 84.48%, after 2 years culture, and the diploid rate got to 11.21%; the rate of3n/2n mosaic got to 2.56%.The changes of ploidy were detected in 96 2-year-old mated triploid oysters pre- and post- spawning season by single marked and ploidy determination alive. After spawning season, the ploidy was changed in 9 oysters (7.76%), of which 8 oysters changed from triploids to 2n/3n mosaics, and 1 oyster from triploid to diploid directly. It showed that spawning did very much in the genetic stability of triploid oyster. The triploid group from mated triploids was obviously bigger than diploids from the same group in shell length, shell width, shell height and body weight(P<0.01). The triploid group was also obviously bigger than mosaic group in shell length and body weight (P<0.05). The mosaics was obviously bigger than diploid group in body weight and shell height (P<0.05).III.Cbromosome composition in mated triploid oystersThe chromosome composition in 2-year triploid oysters was analyzed by chromosome counting. The result showed that, there were 56 triploids (70.0%), 12 mosaics (15.0%), 4 aneuploids (5.0%) and 8 diploids (10.0%) in total 80 mated triploid oysters. These aneuploids included 9 hypotriploids (3n-1=29) and 3 hypertriploids (3n+l=31). There was no obvious difference in the growth between triploids and aneuploids. The amount of mosaics and diploids was very small; it may be the reason that the mosaics and diploids didn't show bad growth.IV.Comparison of the biology characters between triploids and diploidsIn the spawning season, the gonad of mature diploid oysters is plump and milk white, however, the gonadal development of triploid is worse. After spawning, the gonad of diploid is thin and clear, but triploids are not observed to spawn in the spawning season. The gonad of triploid is milk white and opacity. There are no obviously changes in the gonad of triploid. The mantle of triploid is milk white and opacity, and the sideline between mantle and gonad is not obvious. The mantle of diploid oyster is clear, and the sideline between mantle and gonad is obvious. The mantle of triploid is obviously thicker (P<0.01) and wider...