THE BIRTH OF THE ANDROGENETIC HOMOZYGOUS DIPLOID LOACH (Misgurnus anguillicaudatus)

Studies on unisexual development and homozygous diploid are important in fish genetics and breeding. It is an effective way to purify and improve breeds and to produce monosexual fish. Gynogenesis were successful in many fishes, and gynogenetic homozygous diploid adult fish were obtained. But the reports in relation to fish artificial androgenesis are still rare. Androgenetic haploid loach embryos were produced by mechanically removing female nuclei of Paramisgurnus dabryanus eggs which had been fertilized by loach milt. Transplanting these haploid blastula nuclei into P. dabryanus enucleated eggs resulted in 243 gastrula embryos. Chromosome examination of these nuclear transplants indicated that 29.6% of them had duplicate chromosome number. In another experimental group, 5 adults were obtained from 769 nuclear transplanted eggs. Tail fin chromosome examination, muscle lactate dehydrogenase isoenzyme electrophoresis and morphological character all showed that they were androgenetic homozygous diploid loach. On the basis of the characteristics of fish embryonic mitotic cycle, we are of the opinion that the doubling mechanism of the transplanted haploid nuclei is the presence of a DNA duplication in G2 nuclei after being transplanted into the eggs and then their first cleavage occurs. Due to the fact that the shape of pectoral fins indicated two of the five nuclear transplants being female, we are inclined to believe that the sex determination mechanism of loach is female homogamety and male heterogametry. Discussions concerning the reasons for the high mortality of fish haploid embryos and the possibility of applying the androgenetic homozygous diploid method to fish breeding are presented.