Production of Tetraploid Gynogenetic Loach Using Diploid Eggs of Natural Tetraploid Loach, Misgurnus anguillicaudatus, Fertilized with UV-Irradiated Sperm of Megalobrama amblycephala without Treatments for Chromosome Doubling.

The gynogenesis phenomenon in nature mainly appears in the reproduction of fish and invertebrates. So far, gynogenesis has been successfully induced in many fish species with the aid of some physical or chemical methods for chromosome doubling. However, few fish can produce gynogenetic progenies, genetically identical or similar to the somatic cells of the mothers, without a treatment for the doubling of chromosomes, which may be related to apomixis, premeiotic endoreduplication, or premeiotic endomitosis. At present, no studies are available about fish with normal ovarian structures producing gynogenetic progenies that could spontaneously double their chromosomes. According to the analyses of flow cytometry, chromosome number, and microsatellites, we found that, with the use of UV-irradiated sperm of blunt snout bream Megalobrama amblycephala, tetraploid loach Misgurnus anguillicaudatus produced tetraploid gynogenetic progenies without any treatments for the doubling of chromosomes. To determine the genetic relationships of gynogenetic progenies and their maternal parent, microsatellite genotyping was conducted. The results indicated that the reason for spontaneous chromosome duplication in gynogenetic progenies may be cytokinesis or inhibition of the extrusion of the second polar body. This is the first report on fish with normal ovarian structures that can produce gynogenetic progenies which spontaneously double their chromosomes and which are genetically identical or similar to the somatic cells of the mothers.