The ginbunas (Carassius auratus langsdorfii) captured in the Kanto district were exclusively females, and the majority of them showed the triploid chromosome number of 156. A few individuals, however, contained 206 instead of 156 chromosomes in the same district. In this connection, we re-examined the chromosomes of ginbunas collected from Chiba prefecture, using scale epithelial cell cultures and have been able to demonstrate a consistent karyotype in ginbunas with 206 chromosomes; they consisted of 22 pairs of metacentrics, 41 pairs of submetacentrics and 40 pairs of acrocentrics. Consequently, these female ginbunas appeared to represent the 4n lineage.
In order to find out th productive system of the 4n ginbuna, a cross breeding between a female ginbuna (4n) and a male kinbuna (2n) collected from Kasumigaura was made in a series of this study. The development of the cross-bred eggs was normal, and the larvae grew up normaly. All the grown up offsprings were females and similar to the maternal ginbun in their body shape. Chromosome preparations in the offsprings were made from short term lymphocyte cultures obtained from renal tissues. The results of chromosome counts in 6 offsprings examined revealed the modal chromosome number of 206. Comparing the karyotypes of the offsprings with that of the maternal 4n ginbuna, we could not find out any difference among their chromosome constitutions, so far as the morphological analysis is concerned.
Based on the present findings, the most likely explanation would be that the production of the 4n offsprings by a hybrid cross, 4n ginbuna×2n kinbuna, might have arisen by gynogenesis, as has already been pointed out for the production of 3n ginbunas by the authors.