| Research progress, status and meaning of tetraploid breeding of shellfish were reviewed in this paper. Methods and basic principle of tetraploid induction, inductive results, action mechanism of revulsant, influential factors in induction, ploid identification, the biological characteristics of the tetraploid mollusk, and the aneuploid phenomenon of tetraploid breeding were discussed. Problems in mollusk tetraploid breeding were analyzed and prospects were viewed.Tetraploid induction were tested by inhibiting the release of polar body in newly fertilized eggs from diploid or triploid Crassostrea gigas with CB or 6-DMAP. Cytological process in induction were observed and described in this paper. And the survivable juvenile tetraploids were successfully produced by inhibiting one polar body of eggs from triploids that had been fertilized with sperm from diploids.1 , Tetraploid induction in diploidsTetraploid induction by inhibiting polar body I (short treatments-15min) or both polar body I and II (long treatments-30min) of the newly fertilized diploid eggs with CB (0.75mg/L) or 6-DMAP (70mg/L) were conducted. By taking count of chromosome of the embryo period, results were shown as follows: Inductive effect of short treatments (15min) with CB and long treatments (30min) with 6-DMAP were preferable, and the average tetraploid rate of the former embryo was 18.41% and higher than that of long treatments(30min) with CB by about 26.62%;the latter was 17.90% and more 1.17 times than that of short treatments(15min) with 6-DMAP. Furthermore, inductive effect with CB was better than that with 6-DMAP, because tetraploid rates were both relatively high by inhibiting polar body I or both polar body I and II with CB, while tetraploid rate was quite low by inhibiting polarbody I with 6-DMAP.2, Tetraploid induction in triploidsWe selected those individuals with high quality eggs after anatomizing triploid Crassostrea gigas one by one, and then eggs from individual triploid females rather than pooled from a number of females were fertilized and treated according to biological landmarks. That is, when the eggs from individual triploid female showed the first polar body I extrusion or 20-30% polar body I extrusion(as judged by microscopic examination of dividing), the CB (0.75mg/L) or 6-DMAP (70mg/L) treatment began and was discontinued after 15 min. In this experiment, 17 treatments were accomplished, and proportions of tetraploids in 24h larvae ranged from 38.30% to 75.59% for an average of 52.31% by Flow Cytometry(FCM). Thereinto, the average proportion of tetraploids was 58.72% (40.16%-75.59%) or 41.03% (38.30%-45.16%) by inhibiting polar body I or polar body II of the newly fertilized triploid eggs with CB, and 51.97%(38.57%-62.18%)or 58.71%(50.45%-68.87%)by inhibiting polar body I or polar body II of the newly fertilized triploid eggs with 6-DMAP. It is obvious that the effect of CB is better than that of 6-DMAP in inducing tetraploids by inhibiting polar body I and the effect of 6-DMAP is better than that of CB in inducing tetraploids by inhibiting polar body II.3 , Tetraploid breedingIn this experiment, 17 treatments were accomplished, 3645.91 104eggs were used, and the fecundation rates ranged from 14.6% to 99.1% for an average of 71.14%, the average hatch rates was 8.99%, and 162.22 X 104 larvae were obtained; the larvae of the treatment groups growed more rapidly than diploids, but the survival rates were quite low, and after 4 days the average was only 40.48% and at 22 days it was only 2.40%(the range from 0 to 3.33%); at settlement, 2335 juveniles were obtained, and the survival rate was only 0.0049%.The juveniles after settlement were breeded in room till 9 e.o.m, 2003 and since then they had been breeded on the sea. After 8 months 106 juveniles of 6-DMAP and CB treatment groups were analyzed by Flow Cytometry(FCM) and the size of these were measured. The results were shown as follows: the average size of juveniles was2.58 + 0.93cm, 93 tetraploid juveniles were obtained, and the average propo...
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