Chromosomal inheritance patterns of intergeneric hybrids of ictalurid catfishes: odd diploid numbers with equal parental contributions

Hybrid chromosomal compositions of channel catfish Ictalurus punctatus × black bullhead Ameiurus melas and channel catfish × flathead catfish Pylodictis olivaris were analysed by a computer-based method. The karyotype of each hybrid was highly asymmetric, and the diploid numbers and arm numbers were intermediate to the parental types. The hybrid offspring of channel catfish × black bullhead possessed a diploid number of 59 chromosomes, with an arm number estimate of 87. The hybrid offspring of the channel catfish × flathead catfish cross possessed a diploid number of 57 chromosomes, also with an arm number estimate of 87. Nucleolus organizer regions (NORs) were located on a single pair of chromosomes with symmetric staining intensity in channel catfish and in black bullhead, and on a single pair of chromosomes with asymmetric staining intensity in flathead catfish. The channel catfish × black bullhead hybrid had two unpaired chromosomes that stained positively for NORs. The channel catfish × flathead catfish had three unpaired chromosomes that stained positively for NORs. Specific marker chromosomes were identified in each hybrid. There was no evidence of androgenesis, gynogenesis, polyploidy or aneuploidy in the hybrids. Results of this study, plus information reported previously, indicate that chromosomes of ictalurid catfishes are inherited stably in a haploid pattern with an equal contribution to the genomes of F₁ hybrids, even in intergeneric crosses involving divergent numbers of parental chromosomes.