The Observation of Meiotic Union Behavior of Gametophytes Provides a New Basis for Ploidy of Carassius auratus gibelio

Simple SummaryOur study investigates the karyotype of a vital polyploid fish,Carassius auratus gibelio. We found 150 chromosomes with 6 nucleolar organizer regions, suggesting complex chromosomal interactions. Male and femaleC. gibelioshow different chromosome pairings, indicating asynchronous evolution. The formation of two trivalents or two bivalents and two univalents from six NOR bearing chromosomes in maleC. gibeliois considered evidence of being in the process of rediploidization. The presence of only univalents and bivalents in the oocytes of femaleC. gibelioindicates that their cytogenetics are more stable, suggesting that they have completed rediploidization. Our findings contribute to the understanding of the underlying mechanisms and evolutionary outcomes of this species’ genome. They provide relevant insights for further exploration of the reproductive modes of polyploid organisms and breeding strategies.Carassius auratus gibelio, a significant polyploid fish in Chinese aquaculture, can reproduce through both unisexual gynogenesis and sexual reproduction. WhileC. gibeliois known to exhibit polyploidy throughout its lifecycle, whether the homologous pairing of chromosomes is associated with the mode of reproduction remains unclear. Our study determined its karyotype as 2n = 150, comprising 42 metacentric, 24 submetacentric, 6 subtelocentric, and 78 telocentric chromosomes. Using AgNORs, CMA3/DAPI double fluorescence staining, and FISH, we identified six nucleolar organizer regions inC. gibeliochromosomes. FemaleC. gibelioexhibited only univalent and bivalent configurations, while males showed a range of chromosome configurations from univalent to hexavalent. CMA3-positive sites and FISH signals in trivalents spermatocytes hint at homologous triploidization. The formation of two trivalents or two bivalents and two univalents from six NORs bearing chromosomes in maleC. gibeliois considered evidence of being in the process of rediploidization. The presence of only univalents and bivalents in the oocytes of femaleC. gibelioindicates that their cytogenetics are more stable, suggesting that they have completed rediploidization. Asynchronous progression of polyploidization may lead to differences in reproductive patterns between male and femaleC. gibelio. Our results offer cytogenetic insights into the polyploidy and evolution ofC. gibelio, providing foundational cytogenomics data. This study provides relevant references for revealing the distinct reproductive strategies of male and femaleC. gibelio: under stable conditions, gynogenesis enables rapid clonal reproduction and swift population growth, while sexual reproduction enhances the genetic diversity within the population.