First cytogenetic characterization of the sub-arctic marine fish Mallotus villosus (Müller, 1776, Osmeriformes, Osmeridae)

The capelin, Mallotus villosus (Osmeriformes, Osmeridae), is an ecological and commercial key component of the sub–arctic ichthyofauna. Here, we provide the first cytogenetic information on the species based on both conventional karyotyping and chromosomal mapping of 45S and 5S ribosomal genes through fluorescence in situ hybridization (FISH). The capelin genome displayed a diploid number of 54 with the karyotypic formula 26m/sm+28st/a and a fundamental number (FN) = 80. Both classes of ribosomal genes appeared to be spread out to multiple chromosomal locations, i.e. the 45S and 5S rDNA clusters were detected on six and seven chromosome pairs, respectively. A linked chromosomal organization of the major and minor ribosomal genes classes has been visualized in most of the rDNAs chromosomal locations. A comparative analysis of the available cytogenetic data for the family Osmeridae reveals diploid numbers higher than 48 and high fundamental numbers. This suggests that a rearranged karyotype is a shared feature within this family.