Study On Allotriploid Induction In Oyster

Induction of triploidy is of great importance in mollusk breeding,and can be modified further with interspecific hybridization techniques to create allotriploids which may benefit both from triploidization and hybridization.Hybrids, Crassostrea hongkongensis♀×C. gigas♂were studied on fertilization with fluorescent microscope. Hypotonic treatment was used in the allotriploid and C.hongkongensis triploid induction by inhibiting polar body II(PB2)releasing.The fertilization development process,suitable induction parameters,genetic analysis,ploidy investigation,growth and survival during the stage of larval development were discussed in this study.All information would be the foundation for oyster breeding.The main contents consist of the following there parts.1. Cytological observation on cross fertilization of C.hongkongensis♀×C. gigas♂with fluorescence microscope.The fertilization between C.hongkongensis eggs and C. gigas sperm stained with DAPI were observed with a fluorescence microscope.Results proved the possibility of hybridization berween these two diferent geographic species.Clearly parts of sperms from C. gigas could bind and penetrate into the mature eggs of C.hongkongensis which were in prophase or metaphase of meiosis.The rate of crossing fertilization was approximate 35%.With the activation from sperms,eggs finished the first and the second meiotic division and release the first and the second polar body.The male and female pronuclei fused finally,and the diploid zygote nucleus was formed .Most hybrids could devide normally.However, asynchronism and retardance in hybrid development are remarkable, compared with the control group of C.hongkongensis.2 .Induction of oyster allotriploid by hypotonic treatment and nursery.In order to optimize the induction parameters,including the beginning time of treatment,the hypotonic salinity and the duration time,different hypotonic treatments(when 5min,10min,15min,20min,25min,30min,35min,40min,45min,50min after insemination; salinity of 4,6,8,10,12 and 14‰;duration time of 10min,15min,20min,25min)were carried by inhibiting PB2 releasing.Results showed the zygotes treated for 25 min with a hypotonic solution of 10 salinity at 20min after fertilization can yield the highest triploidy rate of 68.65%, and the hatchery rate of 12.71%.No statistical advantages of growth rate and survival rate were found in allotriploid induction groups compared with control groups during larvae development. Larvae survival rate allotriploid and diploid hybrids were (0.1160±0.0234) % and (6.50±1.88) % at the 9th day after insemination. All allotriploid larvae died before metamorphism without forming eyespot or foot.3 .Induction of C.hongkongensis triploid by hypotonic treatment and nursery.The same experimental setting as part 2 was applied to optimize the induction parameters of C.hongkongensis triploid by inhibiting PB2 releasing.Results showed the zygotes treated for 20 min with a hypotonic solution of 10 salinity at 15min after fertilization can yield the highest triploidy rate of 82.06%, and the hatchery rate of 71.44%. The change of induction parameters concernd asynchronism and retardance in hybrid development.Statistical advantages of growth rate was found in C.hongkongensis triploid group compared with diploid group during larvae development.Especially, difference of growth rate was very significant at the 11th day after insemination when the shell length achieved 168μm (P<0.001).