Chromosome banding in salmonid fish: nucleolar organizer regions in Salmo and Salvelinus

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Abstract
Chromosome banding patterns obtained by silver staining (Ag-NORs) were analyzed in 3 spp. of Salmo (rainbow, brown trout and Atlantic salmon [S. gairdneri, S. trutta and S. salar]) and 3 spp. of Salvelinus (brook trout, lake trout and arctic char [S. fontinalis, S. namaychush and S. alpinus]). In rainbow trout and Atlantic salmon the Ag-NORs were found at the secondary constrictions of a single chromosome pair, while in brown trout the Ag-NORs were found on the short arms of 1 or 2 of the 2 longest subtelocentric or acrocentric chromosome pairs. The location of the Ag-NORs was multichromosomal in the 3 Salvelinus species, occurring on one or both members of 4-6 different chromosome pairs in different individuals. The Ag-NOR sites were on the short arms of some acrocentric pairs and at the telomeres of other acrocentric pairs and 1 or 2 metacentric pairs. Chromomycin A3 positive bands were found at the same sites as the Ag-NORs in all species. In the species with multichromosomal location of Ag-NORs, polymorphisms in the size and location of the NORs were extremely common, so that almost every individual fish had a different pattern of Ag-NOR sites.