The distribution and clone composition of silver crucian carp, Carassius sp., a triploid species breeding clonally by gynogenesis, was investigated in Gifu Prefecture, central Japan, using RAPD-PCR together with scale transplants. From red blood cell diameter measurements, 117 fish were demonstrated to be triploid silver crucian carp in a total of 237 crucian carp (Carassius spp.) collected from five branches of the Nagara River, the main stream of the Ibi River and one branch of the Shonai River. Sixty clonal lines could be identified from 115 triploid fish, the percentage of triploids, and number and size of clonal lines being different in each river system. Three clonal lines were confirmed across two or more branches. Apparently the presence of common clonal lines and differences in clone composition between river systems resulted from interchanges between fish populations and local environmental differences within each river system, respectively.
