Chromosome-banding study of the Alaska blackfish, Dallia pectoralis (Euteleostei: Esocae), with implications for karyotype evolution and relationship of esocoid fishes

Abstract

Chromosomes of Dallia pectoralis from two widely separated locations in Alaska (Yukon River system and Colville River) were analyzed by Giemsa staining, C-banding, and Chromomycin A3 fluorescence. The karyotype was redescribed more precisely. The diploid number 2n = 78 was found, but a significant number of cells with 74–77 chromosomes in individuals from the Yukon River indicate chromosomal polymorphism in the species. 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 distribution of heterochromatin was nearly the same, and the number and location of nucleolar organizer regions (NORs) was identical. The variation (71–79) may be attributable to the association of NOR-bearing chromosomes or to chromosomal distinction between populations in the two rivers. The results suggest close relationships among all the species of Umbra, a closer relationship between Novumbra and Dallia than either bears to Umbra, and a possible closer relationship between Umbra and Esox than between Esox and Novumbra plus Dallia.