Studies On Genetic And Reproductive Characteristics Of Autotriploid Fish

Usually, distant hybridization leads to the formation of polyploid, and normal diploids × the tetraploids which was obtained from distant hybridization could produce triploids which possessed many advantages. In this study, the fertile autotriploid fish(FAT) was obtained from red crucian carp(RCC, 2n=100)(♀) × the autotetraploid fish(4n F2, 4n = 200)(♂) and the sterile allotriploid fish(SAT) derived from common carp(CC, 2n=100)(♀) × the autotetraploid fish(4n F2,4n = 200)(♂). Both of them shared the same male parent,while with different reproductive characteristics. It is generally known that the triploids are sterile due to the abnormal chromosome pairing during meiosis. This study evaluated the differences and similarities between FAT and SAT in ploidy level, gonadal structure, phenotype, and 5S r DNA. The major contents are as follows:1、The different ploidy-level of FAT, SAT and their parents were determined with chromosome counting and detection of mean DNA content of blood cells. The results show that both of them were triploids with 150 chromosomes.2、The experiment result of the 2-year-old FAT and SAT gonads histological sections shows that, The ovaries of FATat 2-year-old were normally developed and contained stages II,III, and IV oocytes. However, at 2-year-old, the ovaries of SAT were developed abnormal with a few oogonia having developed into oocytes of phase II. In the testes of 2-year-old male FAT and SAT, there were some spermatogonia and spermatids exsisted in the seminiferous tubules, but no sperm. Moreover,no semen could be squeezed out from these testes.3、At 2 years of age, the measurable and countable traits in FAT and SAT were examined, The results show that: there are differences between FAT and SAT in both measurable and countable traits, thereinto, the significant different between FAT and SAT was the number of lateral scales. The number of lateral scales of FAT(30-31) were intermediate between RCC(28-30) and 4n F2(29-32), and the number of lateral scales of SAT(33-34) were intermediate between CC(36.0) and4 n F2(29-32). Both of them were present hybrid traits.4、The 5S r DNA of 4n F2, FAT and SAT were sequenced and analyzed. Four fragments were identified in the PCR product of 4n F2(203, 340,406 and 484bp), four in FAT(203, 340,406 and 495bp), and four fragments occurred in SAT(203, 340, 406 and 487bp). By the way the specific maternal 5S r DNA sequence class IV(317bp) of CC was not observed in the SAT.In conclusion, this is the first report concerning the fertile autotriploid fish produced by crossing different ploidy parents in vertebrates. The obtainment of fertile autotriploid fish was benefit for reproductive biology and genetic breeding.