STANDARDIZATION OF THE CHANNEL CATFISH KARYOTYPE WITH LOCALIZATION OFCONSTITUTIVE HETEROCHROMATIN AND RESTRICTION ENZYME BANDING

Genetic research of fishes is hampered by lack of standardized karyoty pes and reliable techniques of chromosome banding. The goal of this st udy was to develop a standardized karyotype of channel catfish Ictalar us punctatus by a variety of banding techniques and computer-assisted analysis. Metaphase chromosomes were prepared from cultured leukocytes and kidney cells of adult and juvenile fish. Silver staining and alka li treatment methods were used to reveal nucleolus organizer regions ( NOR) and the location of constitutive heterochromatin (C-bands). Chrom osomes were treated with IO different restriction enzymes, stained wit h Giemsa, and examined for banding patterns. The chromosomal data were analyzed with two computer software packages. The 29 chromosomes were classified into eight distinct groups based on morphology and size. T he NOR were located on a pair of medium-sized submetacentric chromosom es (designated as D-ll); this was consistent among cells from differen t specimens. The C-bands were small and restricted to centromeric regi ons and were useful for homologous pairing. A standard karyotype of CB G-banded chromosomes (C-bands visualized by treating with barium hydro xide and staining with Giemsa) was developed. The restriction enzyme M sc I produced informative banding patterns with dark telomeric bands a nd clear centromeric regions. The enzyme Hind III was most informative , yielding linear banding patterns that were consistent between member s of homologous pairs. Our study provides a fundamental step in genome mapping of fishes. Standardization of the channel catfish karyotype a nd chromosome banding will facilitate physical mapping of genes in thi s important culture species.