Gynogenesis Induced And Histological Observation On Gonadal Sex Differentiation In Barfin Flounder (Verasper Moseri)

Barfin flounder(Verasper Moseri) is a marine flatfish species which has an important commercial value.It is essential for Japan aquaculture industry.Recently,natural resources is at low ebb.This species is therefore a strong candidate for aquaculture to mitigate fishing impacts and stabilize seafood supply.Because female flounder reach substantially larger sizes than males, all-female culture is desirable for commercial aquaculture.Hence,athorough understanding of sexual development,its timing and regulation by temperature is essential for optimization of flounder aquaculture.Barfin flounder was a kind of important marine fish,which growed fast,tasted delicious and had great nutritional value.Barfin flounder females growed bigger and mature later than males,it was reported that females growed 1-2 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 barfin flounder.In this research,the induction of all-female populations was carried out by gynogenesis methods,gynogenesis embryonic development and sex differentiation of barfin flounder were observed.We also tested the optimum parameters for UV irradiation of sperms, suppression of second polar body release and for suppression of the first cleavage.The results showed as follows:1.The effects of UV irradiation on genetic inactivation of sperms of Verasper moseri were examined.Using two paralleled UV lamp(20W each),the optimal time of UV irradiation for effective inactivation of Verasper moseri sperms was 60s when the distance between sperms and UV lamp was 10cm.Gynogenetic haploid,which was proved by the haploid characteristic,were obtained under these irradiation conditions.The hatching rates of the eggs exhitited typical "Hertwing Effect".2.The parameters of induction of gynogenetic diploid in Verasper moseri were optimized. Chromosome diploidy wes achieved by suppression of the second polar body release by early cold shock applied 5-17min after fertilization at -1.5-3℃with 30-150min durations.The optimal cold shock was at -1.5℃that was applied at 11min after fertilization and lasted for 60min.3.Haploid was obtained by flounder sperm that was destroyed by ultraviolet radiation activating eggs of barfin flounder;gynogenetic embryo was obtained by sperm that was destroyed by ultraviolet radiation activating eggs of barfin flounder and cold shock;general diploid was obtained by sperm and eggs seminating.The Embryonic development speed of different groups showed:Multicelled stage ago,haploid embryos development rate was slower than normal embryos.Multicelled stage was the same time,they took 14 hours.High blastula of was haploid embryos was slower than normal embryos,besides late gastrula neurula stage,formation of eyelens stage,haploid embryos development rate was always slower than normal embryos;the larva shown haploid syndrome;there were no significant differences in embryonic development between gynogenesis diploid and normal diploid individuals.However,different time of every stage was found in embryonic development among gynogenesis diploid,normal diploid and haploid individuals.4.Barfin flounder belonged to the differentiated species of gonochoristic fish and ovary differentiated earlier than that of spermary.On the 20th day post-hatch(dph),gonad anlage was made of PGC and genital ridge.The germ cells proliferated rapidly at about 60 dph.On the 80^th,the gonad was differentiated,the oviposition plate rudiment was formed;on the 120th the anlage of the efferent duct was found,which would develop into testis.Oocytes in early meiosis were first observed from the ovary on 100th dph,while the primary spermatocytes were found after 120th dph.