Cytology Study On The Fertilization Of F₁Hybrids O F Red Crucian Carp（♀）×Blunt Snout Bream（♂）

Distant hybridization is the most effective and direct way in all means which can obtain polyploidy hybridization, there are increasingly ways have already prove the method is steady and good. The distant hybridization of fish is include different specie、different subfamily even different genus. This method can effectively alter the hybrid of offspring’s gene configuration and phenotype, because of their giant difference of gene configuration. This study observe triploid hybrid of the offspring of cross the red crucian carp(Carassius auratus red var.)(RCC)(?) x blunt snout bream(Megalobrama amblycephala)(BSB)(?) as well as teraploid hybrids in fertilization of study with the method of paraffin section. Results show that:Firstly, The sperm of BSB enter into the mature egg of RCC which at the metaphase of the secondary meiosis through micropylar canal. There are, however, several sperms simultaneously come into the micropylar canal, but the mode of fertilization is monospermy. Secondly, when fertilized eggs developed in the metaphase of the secondary meiosis at8minutes after insemination, we observe that all of the nuclear material were keep into the fertilized egg, at the same time, the second polar body was extruded without any nuclear material, we speculate that this propably is the cause of forming polyploidy. Thridly, the forming of female-male pronucleus and the progress of conjugation is similar with bony fish. Forthly, the result present that the first maturation division of some fertilized eggs was postponed and inhibited at40min after insemination. We found a zygote nucleus bigger than normal one in optical microscope after12minutes later, this can further prove that endoreplication may be the cause of forming tenaploid RB F1.This study provide new evidence and clue for researching the mechanism of polyploidy fish which were caused by the distant hybridization.