Abstract
The catfish family Siluridae contains 107 described species distributed in Asia, but with some distributed in Europe. In this study, karyotypes and other chromosomal characteristics of 15 species from eight genera were examined using conventional and molecular cytogenetic protocols. Our results showed the diploid number (2n) to be highly divergent among species, ranging from 2n = 40 to 92, with the modal frequency comprising 56 to 64 chromosomes. Accordingly, the ratio of uni- and bi-armed chromosomes is also highly variable, thus suggesting extensive chromosomal rearrangements. Only one chromosome pair bearing major rDNA sites occurs in most species, except for Wallago micropogon, Ompok siluroides, and Kryptoterus giminus with two; and Silurichthys phaiosoma with five such pairs. In contrast, chromosomes bearing 5S rDNA sites range from one to as high as nine pairs among the species. Comparative genomic hybridization (CGH) experiments evidenced large genomic divergence, even between congeneric species. As a whole, we conclude that karyotype features and chromosomal diversity of the silurid catfishes are unusually extensive, but parallel some other catfish lineages and primary freshwater fish groups, thus making silurids an important model for investigating the evolutionary dynamics of fish chromosomes.
Highlights
The family Siluridae is a lineage of freshwater catfishes widely distributed through Eurasia, but with the highest diversity in South and Southeast Asia [1]
Extensive chromosomal variability of 5S rDNA loci has been described for several other fish groups ([21,22,79,82]; for review, see the work of [74])
The absence of a direct correlation between higher 2n numbers and amplification and dispersion of the 5S rDNA clusters is an indication that this rDNA class was not the unique trigger for the chromosomal rearrangements occurring among the respective silurid species
Summary
The family Siluridae is a lineage of freshwater catfishes widely distributed through Eurasia, but with the highest diversity in South and Southeast Asia [1]. Siluridae includes one of the largest freshwater fish species—Silurus glanis—which commonly reaches 2 m in size and over 300 kg in weight [14], and is highly valued in the food market [15]. Several other species, such as Micronema cheveyi, Phalaconotus apogon, P. bleekeri, Wallago attu, and W. micropogon, comprise important food sources [16] or are ornamental fishes, like the glass catfish Kryptopterus bicirrhis [17]
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