Chromosomal studies of germ cells in diploid and polyploid fish produced by distant crossing

By observing the chromosomal spreads of germ cells and tissue sections, we studied the chromosomal spreads of germ cells in diploid and polyploid fish produced by distant crossing. The samples covered the second generation of hybrids of red crucian carp (Carassius auratus red var.)(♀) × common carp (Cyprinus carpio) (♂)(2n=100)(F_2), allotetraploid hybrids of red crucian carp(♀) × common carp(♂)(4n=200), triploid hybrids of gold fish(♀)× allotetraploid(♂)(3n=150), the second generation of the gynogenetic progeny of allotetraploid hybrids(G_2)(2n=100), and the common carp(2n=100) used as a control. The results demonstrated that chromosomal number of spermotogonia in common carp was equal to that of their somatic cell (2n=100), while the chromosomal number of germ cells in diploid hybrid fish and polyploid hybrid fish had doubled obviously, and the frequent of chromosomal doubling in spermotogonia of F_2 appeared especially high, accounting for 21.6% of all examined chromosomal spreads, which provided directly cytological evidence for the production of unreduced diploid gametes in F_2 and also indicated that distant crossing was an important factor to lead to chromosomal doubling in germ cell. This research had important significance in studies on the formation of polyploidy fish and fish breeding.