Mechanisms on Occurrence of Spontaneous Polyploid Fish and Their Application as Resources for Breeding

本研究旨在阐明泥鳅多倍体的发生机制和遗传方式。1.泥鳅四倍体（4n）的自发性没有观察到从河流，但从鱼贩子。在野生和养殖的泥鳅标本中发现了少量的三倍体（3n）泥鳅。2.正常二倍体（2n）泥鳅卵经紫外线照射精子受精后所产生的雌核发育后代在摄食前死亡，而4n泥鳅卵所产生的雌核发育后代则能存活。用4n种双棘鳅卵不经二倍体化处理，获得了有活力的雌核发育细胞。这些观察结果表明，4n泥鳅和棘泥鳅是真正的四倍体，具有四套同源染色体。3.用自发的4n和2n正反交获得了活的3n泥鳅。通过抑制4n × 2n ×卵的第二极体的排出，培育出5n泥鳅。3n和5n的雌虫都有成熟的卵子，而雄虫没有有功能的精子。杂交（3n* × 2n *、5n* × 2n *）和紫外线诱导雌核发育的后代均正常存活。4.在3n雌虫中观察到两种类型的卵，大的和小的。大卵的出现频率在雌虫之间有差异。5.生育力在3n和5n女性和3n和5n的后代的活力表明存在不寻常的配子发生，以防止形成非整倍体卵子和精子。

The present study was made to clarify mechanisms on occurrence and inheritance manner of polyploids in loach fish. 1. Spontaneous tetraploid (4n) loach Misgurnus anguillicaudatus were not observed in the specimens obtained from river, but in those from a fish dealer. Small number of triploid (3n) loach were seen in the specimens from wild origin as well as fish farmers. 2. Gynogenetic progeny produced from eggs of normal diploid (2n) loach after fertiltzation with UV irradiated spermatozoa died before feeding, while those from eggs of 4n loach could survive. Viable gynogens were produced from the eggs of 4n race of spinous loach Cobitis biwas without diploidizing treatment. These observations conclude that 4n loach and spinous loach are true tetraploidy having four sets of homologous chromosomes. 3. Viable 3n loach were produced from reciprocal hybridizations between spontaneous 4n and 2n. 5n loach were produced by inhibiting the 2nd polar body extrusion in 4n*x2n* eggs. Both 3n and 5n females had mature eggs, While no male had functional spermatozoa. Offsprings developed from hybridizations (3n*x2n*, 5n*x2n*) and UV-induced gynogenesis were normal and survived. 4. Two types of eggs, large and small, were observed in 3n female. Frequency of large eggs was different among females. 5. Fertility in 3n and 5n females and viability of offsprings from 3n and 5n suggest presence of unusual gametogenesis to prevent formation of aneuploidy eggs and spermatozoa.