Gynogenetic diploids were produced from the eggs of natural tetraploid loach Misgurnus anguillicaudatus (Pisces: Cobitidae) without any manipulation for chromosome duplication. When eggs of a four-year-old diploid gynogenetic individual were fertilized with spermatozoa of specimens from normal diploid and natural tetraploid lines, viable diploid and triploid progeny were produced, respectively. Thus, egg nucleus of the diploid gynogen is haploid. In the gonads of diploid progeny, diploid (2n = 50) and tetraploid (4n = 100) mitotic metaphases were observed. The majority of oocytes (76%) showed regular 25 bivalents as in normal diploids, but the other 16% showed a few univalents. The remaining 8% exhibited about 50 bivalents, suggesting chromosome duplication by premeiotic endomitosis. In the testes, a few spermatocytes (6%) showed normal 25 bivalents, but 86% contained various number of univalents and the remaining 8% contained about 50 bivalents. No peaks of spermatozoa were identified in the testis by flow cytometry. In the triploid progeny, triploid (3n = 75) and hexaploid (6n = 150) mitotic metaphases were observed in both ovaries and testes. Most meiotic figures (about 90%) contained approximately 25 bivalents and 25 univalents in both sexes; the rest contained approximately 75 or more bivalents. Spermatozoa were not identified in the testis by flow cytometry. Thus, the diploid males between the diploid gynogens and common diploid, and both sexes of triploids between the diploid gynogens and tetraploid, show aberrant meioses such as frequent formation of univalents, but the diploid females seem to be less affected.
Extensive karyotype variation was found in both somatic and meiotic cells of the progeny in a laboratory-reared family of the loach Misgurnus anguillicaudatus. Only one of seven individuals examined showed the standard karyotype, 2n = 50 comprising 10 metacentrics, 4 submetacentrics and 36 telocentrics. However, the other six individuals exhibited hyperdiploid karyotypes due to the presence of additional telocentrics and micro-chromosomes, resulting in chromosome numbers 2n = 51 to 53, or 58 plus 0 to 5 micro-chromosomes within or between individuals. Such inter- and/or intra-individual variation in chromosome number was also observed in primary spermatocytes of three males with an increase of bivalents and univalents involving additional telocentrics, although micro-chromosomes were seldom paired. Accumulation of additional chromosomes was apparent in spermatogonia and spermatocytes with greater incidence than in somatic cells. Euploid and aneuploid loaches were not discriminated by the external morphology, suggesting the observed additional chromosomes to be genetically neutral.