Studies On The Main Biological Characteristics Of The F₁Hybrids Of Bleeker’s Yellow Tail（Xenocypris Davidi Bleeker,♀）×Topmouth Culter（Erythroculter Ilishaeformis Bleeker,♂）

Distant hybridization of fishes is the distant mating of two different kinds of fishes which may involve crosses between different species, subfamilies or families. Distant hybridization could combine parental advantages and obtain heterosis such as sharp, growth rate, survival rate, or disease resistance. So distant hybridization is an important method in fish breeding and trait improvement. In addition, It’s also generally accepted that hybridization plays a significant role in the ignition of polyploidy. Through distant crossing, diploid hybrids of Bleeker’s yellow tail(Xenocypris davidi Bleeker, YT♀,2n=48)×Topmouth culter (Erythroculter ilishaeformis Bleeker, TC♂,2n=48) were successfully produced. And studies of these hybrid offspring on ploidy-level, chromosomal number, mean DNA content, appearance, the organization and variation of5S rDNA, location of5S rDNA on the chromosomes and Sox genes were conducted, and the major contents are as follows:1) Through distant crossing between female Bleeker’s yellow tail and male Topmouth culter, the hybrids were successfully obtained. The hybrid offspring were proved to be diploid (2n=48) by the determination of chromosome counting and detection of mean DNA content of blood cells. At2years of age, the measurable in diploid hybrids were examined, which showed that some traits present more similarity to the female parents and some to the male parents, also some in between the parents, showed the hybrid characteristics, and some higher than the parents. Gonadal paraffin method showed that female diploid hybrids were fertile with normal ovarium.2) The5S rDNA of the hybrid and their parents were sequenced and analyzed, and the Chromosome localization was also done Through fluorescence in situ hybridization (FISH). There were two monomeric5S rDNA classes (designated class I:188bp; and class II:221bp) in YT and two monomeric5S rDNA classes (designated class I:188bp, and class Ⅲ:286bp) in TC. The hybrids not only inherited class I and class III from their parent, but also generated a new5S rDNA sequence (designated classIV:212bp). The sequence of class II was not found in the hybrid offspring. Furthermore, the localization of188bp5s rDNA probe t revealed there is two signals in a haploid chromosome set, one in the largest submetacentric chromosome and the other in a subterminal chromosome. The results obtained here indicated that the hybrid inherited most of the5S rDNA unit from their parent, and the variation was happened at the same time.3) Against the conserved HMG-box of Sox genes, one pair of degenerate primers were designed and synthesized to amplify the genomic DNA of hybrid offspring and their parents, and the comparative analysis was also proceeded. There were three DNA fragments of Sox genes in YT, including Soxl(215bp), Soxll(215bp) and Sox9(710bp). Similarly, there were three DNA fragments of Sox genes in TC, including Soxl (215bp), Soxll(215bp) and Sox9(726bp). However, the hybrids inherited all the Sox fragments from their parents, including Soxl(215bp), Soxll(215bp), Sox9(710bp), Sox9(726bp). The results showed that YTTC was the hybrid from Bleeker’s yellow tail and Topmouth culter.