Spontaneous diploidization of maternal chromosome set in ornamental (koi) carp, Cyprinus carpio L.

Summary An unusually high frequency of spontaneous diploidization in a maternal chromosome set (SDM) was discovered in one ornamental carp (koi) female in an experiment on these fish for induced gynogenesis. Spontaneous appearance of diploid embryos in the gynogenetic offspring (intact eggs × irradiated sperm) and appearance of triploids among control fish (intact eggs × intact sperm) obtained from koi female and males of edible carp indicated spontaneous diploidization of maternal chromosomes (SDM). Possible cytological processes causing this phenomenon are discussed.