CYTOGENETICS, CYTOTAXONOMY AND BIOCHEMICAL GENETICS OF HUCHONINE SALMONIDS

The huchonines are a small, ancient group of salmonids comprising the genera Brachymystax (monotypic) and Hucho (4 species). The chromosomes of huchonine salmonids have been poorly studied so far (7 reports on 3 species only). The karyotypes of H. ishikawai and H. bleekeri are co mpletely unknown. The available data (both published and unpublished) indicate: 1) a small extent of chromosomal polymorphism (B. lenok, H. hucho, H. perryi); 2) the presence of 4 pairs of small metacentrics - huchonine marker elements (B. lenok, H. hucho); 3) the presence of sex -related, quinacrine positive heterochromatin suggesting a sex chromos ome system of XX/XY type (H. hucho); 4) the polymorphic NORs are local ised on the ends of shorter arms of 1 subtelocentric chromosome pair ( H. hucho, H. perryi); and 5) an unusually high content of C-positive h eterochromatin (H. hucho). The values of 2n, which range from 2n = 90 - 92 in B. lenok and 2n = 82 84 in H. hucho to 2n = 62 in H. perryi, s uggest a similar trend of parallel karyotype differentiation as report ed in phyletic lines of salmonids. The biochemical and molecular genet ics aspects are relatively unknown considering that salmonids are the most thoroughly studied fish group in this respect. However, the limit ed data available indicate that: 1) isozyme patterns of huchonines are much more simple (being rather monomorphic) than in other salmonids. probably representing ancestral enzymatic forms; 2) high variability a mong different populations of Brachymystax lenok suggests a more compl ex specific status of these populations; 3) that huchonines were the f irst phylogenetically separate from other salmonid lineages; and 4) Hu cho and Brachymystax are genetically more closely related than are the se genera and Hucho (Parahucho) perryi, suggesting their distinct evol utionary history.