CHROMOSOMAL NOR PHENOTYPES IN NORTH-AMERICAN PIKES AND PICKERELS, GENUS ESOX, WITH NOTES ON THE UMBRIDAE (EUTELEOSTEI, ESOCAE)

A comparison was made of the localization of nucleolar organizer regio n (NOR) sites in the karyotypes of the North American pikes and picker els Esox lucius, E. masquinongy, E. niger, and the two subspecies of E . americanus (Esocidae). NORs were located by silver staining or chrom omycin A(3) fluorescence. The study revealed that the position of chro mosomal NORs in all Esox taxa examined was the same: the pericentromer ic region of one middle-sized chromosome pair. The same NOR phenotype was found previously in a related European species, Umbra krameri (Umb ridae), and in U. pygmaea, one of the two North American representativ es of the genus. The NOR phenotype of the remaining North American spe cies (U. limi) is different. It is hypothesized that this kind of NOR phenotype, shared by two phyletic lineages in the Esocae, represents a n ancestral character for the members of that group.