Studies On The Biological Characteristics Of The Triploid Progeny Of Carassius Auratus × Xenocypris Daviodi Bleeker

Distant hybridization refers to the hybridization between two different species,genus and higher classification levels.Usually,distant hybridization is often accompanied by the appearance of polyploidy.The hybrid offspring(GFYT)were obtained directly from the cross of goldfish(Carassius auratus,abbreviated as GF,2n=100,♀)and Bleeker’s yellow tail(Xenocypris daviodi Bleeker,abbreviated as YT,2n=48,♂).In this paper,the biological characteristics of hybrids and their parents were analysed,the main contents were shown as follows:1.The distant hybridization of female goldfish and male yellow-tailed mackerel had high fertilization rate and hatching rate,which were 75.3% and 64.6% respectively.However,there were no surviving offspring in the cross of goldfish(♂)×Bleeker’s yellow tail(♀).The ploidy of offspring and their parents was detected by chromosome preparation of kidney cells and mean DNA content of blood cells.The results showed that GFYT were triploid fish with 124 chromosomes(3n =124).Four progenies were obtained in GFYT,which were cinerous single-tailed progeny,cinerous double-tailed progeny,red single-tailed progeny and red double-tailed progeny respectively.2.Fluorescence in situ hybridization(FISH)was performed on the chromosomes of the offspring and parents using the probe of crucian carp-specific repetitive sequence(263 bp,JQ086761).The results showedthat the chromosomes of goldfish were labeled with fluorescent signals,and the chromosomes of yellow-tailed scorpion were not labeled,while the GFYT had 100 chromosomes labeled with fluorescent signals and 24 chromosomes were not.It indicated that there were two sets of chromosomes from GF and one set of chromosomes from YT in hybrid triploid offspring.3.The measurable and countable traits of one-year-old goldfish,Bleeker’s yellow tail and GFYT were analysed.In the quantitative traits,The body high/body length and the head length/body length of GFYT was between the male parent and the female parent(P<0.05),reflecting the heterozygosity of the offspring;The body length/full length ratio was biased toward the male parent(P>0.05),showing short tail characteristics;while the head height/head length,tail stalk height/tail stalk length biased to the female goldfish(P>0.05),showing the characteristics of small head and short tail.In countability traits,GFYT were similar to the female parent.4.The gonads of one-year-old GFYT were analysed by histological section,in situ apoptosis detection,transmission electron microscopy and expression of apoptosis-related gene P53 were analyzed.The results exhibited that GFYT had two types of gonad structure,including testicular gonad and adipose gonad.By using ultrastructure and in situ apoptotic detection,spermatocyte apoptosis and degeneration wereobserved in testicular gonads.The expression of P53 in testis was significantly higher than that in other tissues and red crucian carp(P <0.05).5.The expression of gametogenesis-related genes Dmc1,Spo11,Rad51,Mns1,Meig1.The results showed that the expression levels of Dmc1,Spo11 and Rad51,in the testis of GFYT were significantly higher than those in the testis of red crucian carp(P < 0.05).Mns1 and Meig1 in the testis of GFYT were significantly lower than those in the testis of red crucian carp(P < 0.05).The results of this abnormal expression were closely related to the abnormal development of gametes.6.The genetic variation of nuclear gene sequences in GFYT was analyzed by Sox-HMG DNA and 5S rDNA molecular markers.Cloning and Sequencing of Sox-HMG DNA fragments showed that heterozygosity of the source of the genetic information of the GFYT genome.The results of sequencing of 5S rDNA showed that the GFYT contained 188 bp and206 bp 5S rDNA structural units of YT and 340 bp and 480 bp 5S rDNA structural units of GF,which showed hybridization characteristics.In this study,the GFYT were obtained from the cross of goldfish(♀)×Bleeker’s yellow tail(♂).This method of directly cultivating sterile triploid fish by one-step hybridization was of great significance in fish genetics and breeding.Furthermore,these results not only provided guidance for fish breeding,but also provided important evidences for thestudy of distant hybridization,polyploid formation and reproductive mechanism.