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. 四倍体自发性泥鳅（Misgurnus anguillicaudatus）未在河流中发现，但在鱼商处发现。在野生和养殖的泥鳅标本中均发现少量三倍体泥鳅。2. 正常二倍体（2n）泥鳅卵与紫外线照射的精子受精后产生的雌化子代在摄食前死亡，而4n泥鳅卵产生的雌化子代可以存活。在不进行二倍体化处理的情况下，从4n种棘泥鳅的卵中产生了可存活的雌核细胞。这些观察结果表明，泥鳅和棘泥鳅是真正的四倍体，具有四组同源染色体。3. 通过自发4n和自发2n的互反杂交，产生了可活的3n泥鳅。通过抑制4n*x2n*卵的第2极体挤压产生5n泥鳅。3n和5n雌性都有成熟的卵子，而没有雄性有功能的精子。杂交（3n*x2n*, 5n*x2n*）和紫外线诱导的雌核发生后代正常且存活。4. 在3n雌卵中观察到大卵和小卵两种类型。大卵的出现频率在雌性之间存在差异。5. 3n和5n雌性的生育能力以及3n和5n后代的生存能力表明存在不寻常的配子发生，以防止非整倍性卵子和精子的形成。

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.