CHROMOSOME-BANDING STUDY OF THE ALASKA BLACKFISH, DALLIA-PECTORALIS (EUTELEOSTEI, ESOCAE), WITH IMPLICATIONS FOR KARYOTYPE EVOLUTION AND RELATIONSHIP OF ESOCOID FISHES

Chromosomes of Dallia pectoralis from two widely separated locations i n Alaska (Yukon River system and Colville River) were analyzed by Giem sa staining, C-banding, and Chromomycin A(3) fluorescence. The karyoty pe was redescribed more precisely. The diploid number 2n = 78 was foun d, but a significant number of cells with 74-77 chromosomes in individ uals from the Yukon River indicate chromosomal polymorphism in the spe cies. The diploid chromosome number of individuals from Colville River was constant (2n = 74). Colville River individuals had one more pair of metacentrics than Yukon River individuals with 2n = 76. The distrib ution of heterochromatin was nearly the same, and the number and locat ion of nucleolar organizer regions (NORs) was identical. The variation (71-79) may be attributable to the association of NOR-bearing chromos omes or to chromosomal distinction between populations in the two rive rs. The results suggest close relationships among all the species of U mbra, a closer relationship between Novumbra and Dallia than either be ars to Umbra, and a possible closer relationship between Umbra and Eso x than between Esox and Novumbra plus Dallia.