| Half-smooth tongue-sole(Cynoglossus semilaevis) females growed bigger and mature later than males,it was reported that females growed 2～3 times faster than males,in other words its growing taked on sexual otherness.So the production of all-female stock would be of significant benefit for aquaculture of half-smooth tongue-sole.In this research,histological methods were used to observe the sex differentiation of half-smooth tongue-sole,providing the scientific foundation for sex reversal.The induction of all-female populations was carried out by marination treatment,using estradiol-17βwith concentration of 1μg/L,3μg/L,10μg/L and 30μg/L.In the period of female induction,it was essential to observer the sex differentiation of the treated groups,the growth and the mortality rate.It was reported that the triploid populations growed faster and bigger than the normal diploid in some teleosts.So the triploid induction of tongue sole(Cynoglossus semilaevis) with cold shock method were made.Embryonic development of haploid,triploid,gynogenetic diploid and normal diploid were observed.This would provide the basic study material for the growth comparison between the triploid and the normal diploid stock.The results showed as follows:(1) Half-smooth tongue-sole belonged to the differentiated species of gonochoristic fish and ovary differentiated earlier than that of spermary.On the 65th,the gonad was differentiated,the oviposition plate rudiment was formed,then the dorsal edges of these gonads began to extend laterally and they eventually fused to form the ovary;on the 70th the anlage of the efferent duct was found,which would develop into testis.Oocytes in early meiosis were first observed from the ovary after 100th dph,while the primary spermatocytes were found on 90th dph.(2) A chi-squared analysis on sex ratios in each of the control groups showed they were significantly different from 1:1 and they were not significantly different from each other. Furthermore,chi-squared analyses between duplicates of each treatment revealed their sex ratios were not significantly different.And the 1μg/L,3μg/L,10μg/L and 30μg/L treatments yielded 74%,82%,88%and 97%female ratios respectively,it indicated that the endocrine manipulation to half-smooth tongue-sole(Cynoglossus semilaevis) was effective.In the study of hormomal sex reversal of half-smooth tongue-sole,it was showed that 17β-Estradiol could accelerate the ovarian differentiation,but delayed the spermatic differentiation.The ovarian differentiation in the E2-treatment group was earlier for 5 days than which of the control group;while the spermatic differentiation was later 20 days than which of the control group.This might relate to the effect of inner gonadal estrogen to gonadal differentiation,the outside estrogen might stimulate the gonad, which would increase the production of inner gonadal estrogen.It also revealed that 17β-Estradiol did not show negative influence to early growth and cumulative mortalities.The cumulative mortalities of treatment groups approximated 2%,which were not significantly different from the blank treatment.And there was also no difference of the growh dates between the blank and the treared groups.It was necessary to lucubrate continually whether such fish would be suitable for commercial culture.(3) The parameters of induction of gynogenetic diploids in half-smooth tongue-sole were optimized.It showed that the time of the starting treatment,the temperature of the cold shock and the duration of the cold shock would affect the hatching rate of the gynogenetic diploids. Chromosome diploid was achieved by suppression of the second polar bady release by early cold shocks applied 2～6 min after fertilization at 22±0.5℃with 10～30 min durations.The optimal cold shock was at 5±0.5℃that was applied at 3 min after fertilization and lasted for 20 min.Then the triploid was induced by cold shock treatment with the optimal parameters in the gynogenetic diploid.Then the triploidy was proved.And the impregnation rate and the hatching rate were compared between the normal diploid and the triploid group.(4) The Embryonic development speed of different groups showed:the normal diploid group developed faster than the gynogenetic diploid group,the gynogenetic diploid group developed faster than the triploid group,and the haploid group were slowest.A high frequency of abnormality, particularly body flexion and the organ differentiation were found in the haploid embryos.The embryos of gynogenetic diploid and triploid had basically the same process with the normal diploid embryos.There were no significant differences in embryonic development among gynogenesis diploid,triploid and normal haploid individuals.However,different time of every stage was found in embryonic development among gynogenesis diploid,triploid and haploid individuals. |
