| Research progress of triploid breeding of shellfish was reviewed in this paper. Methods and basic principle of triploid induction, influential factors in induction and the biological characteristics of the triploid mollusk were discussed. Problems in mollusk triploid breeding were analyzed and prospects were viewed. Hypotonic treatment was used in triploid induction in Chlamys farreri by inhibiting polar bodyⅡ(PB2) releasing. The suitable induction parameters were studied. Triploid group and diploid group were designed to research the growth of larva. Four different triploid induction methods were compared including hypotonicity,6-DMAP,cold shock and heat shock. Also the ultrastructure of fertilized eggs with hypotonic treatment were observed with scanning election microscopic (SEM) and transmission electron microscope(TEM).The main contents consist of the following parts.1. Study on the suitable induction parameters of triploid Chlamys Farreri with hypotonic treatment.In order to optimize the induction parameters, different hypotonic treatments, including salinity (8-20‰),initial treating time (15～40 min after fertilization), and duration time(10～25 min), were tested at 20℃water temperature. The Results indicated that the optimal hypotonic treatment was 30 min after fertilization,the hypotonic solution of 14‰salinity with 20 min treatment,which can resulted in the highest triploidy rate which was up to (92.36±2.41)%.2. Spat cultivation in triploid Chlamys FarreriTriploid Chlamys Farreri induced by hypotonic treatment used the optimized induction parameters.The triploid group showed obvious growing advantage in the larvae stage(P<0.01), the growing speed of triploid larvae was rapid, and the shell length was longer when it growed to metamorphosis. The triploidy rate of initial D-shape larvae was 90.15%, and it dropped to 60.92% when attached.3. The comparison triploid induction in Chlamys Farreri by hypotonic treatment with other treatment methodsFour different triploid induction methods were compared.①ypotonic Treatment: Triploid Chlamys Farreri induced by hypotonic treatment used the optimized induction parameters;②6-DMAP:Initial treatment time when the first polar body occupied 40-50%,60mg/L of drug concentration,15 min of treatment duration;③Heat shocked:Heat shocked for 15 min at 30℃, initial treatment time when the first polar body occupied 40～50%;④Cold shocked:Cold shocked for 20 min at 1℃, initial treatment time when the first polar body occupied 40～50%. Hypotonic treatment can resulted in highest triploidy rate which was up to (91.43±4.14)%;6-DMAP treatment was up to (91.25±3.49)%; heat shocked and cold shocked were up to (25.85±4.94)% and(21.86±2.04)%.Comparison of triploidy rate showed no significant difference between the treatment of hypotonicity and 6-DMAP(P>0.05),but there was significant difference between the treatment of hypotonicity and temperature shock(P<0.01).4. The comparison triploid induction in Chlamys Farreri by hypotonic treatment with different salinity treating solutionsDifferent hypotonic treatments were tested at 20℃water temperature.,including KCl treating solution, NaCl treating solution,and Seawater dubbed treating solution.The three groups can resulted in the triploidy rate which was up to (90.01±3.27)%, (90.07±2.64)%,and (91.43±4.14)%,and there was no significant difference(P>0.05).5. The ultrastructure observation of fertilized eggs in Chlamys Farreri induced with hypotonic treatment.The change of fertilized eggs'ultrastructure before and after hypotonic treatment were observed by TEM and studied comparelly. Result showed that the ultrastricture of fertilized eggs changed under the influence of hypotonic treatment:The triploid fertilized eggs showed obvious expand,and the bulk was larger,the shape was not so regular.The fertilized eggs repaired itself for a certain extent after being dipped in the natural seawater for a period of time:The shape becomed regular, and the bulk showed no significant difference between the triploid and the normal.The change of fertilized eggs'ultrastructure before and after hypotonic treatment were observed by SEM and studied comparelly. Result showed that the ultrastricture of fertilized eggs changed under the influence of hypotonic treatment:Egg membrane was destroyed. Plasma membrane crimpled and dissolved partly. Enchylema was sparse. The yolks were crimpled. The fertilized eggs repaired itself for a certain extent after being dipped in the natural seawater for a period of time:Plasma membrane got more level up.
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