Karyotypic diversity and evolution of seven mahseer species (Cyprinidae) from India

Abstract

Mahseer is a group of fish species that are well known as food and game fishes. The taxonomyof the mahseer species is confusing owing to the morphological variations and habitat adaptation.Detailed karyomorphological investigations have been carried out in seven species of mahseer, usingkaryotyping, Ag-NOR and fluorescent staining techniques. The basic diploid chromosome num-ber (2n), in all mahseer species, was observed to be 100; however, the karyotype formula variedamong the species, which were recorded as: 20m + 14sm + 22st + 44t (fundamental arm num-ber, FN = 134) in Tor khudree; 22m + 24sm + 24st + 30t (FN = 146) in Tor mussullah; 12m +22sm + 14st + 52t (FN = 134) in Tor putitora; 20m + 24sm + 24st + 32t (FN = 144) in Tor tor ;20m + 30sm + 24st + 26t (FN = 150) in Tor chelynoides; 20m + 20sm + 20st + 40t (FN = 140) inTor progeneius; and 20m + 18sm + 14st + 48t (FN = 138) in Neolissochilus hexagonolepis. Silverstaining of the chromosomes revealed the presence of multiple nucleolar organizer regions (NOR) inthese mahseer species. The highest number of NORs was observed in T. tor (four pairs of chromo-somes), whereas the other six species possessed Ag-NOR signals on only two pairs of chromosomes.Although chromomycin A3(CMA3) staining induced bright fluorescence signals on same Ag-NORssites, with CMA3, one additional signal was observed on the p arm of subtelocentric chromosomesin T. tor, T. chelynoides, T. progeneius and N. hexagonolepis, which may indicate the presence ofinactive NOR in these species. The information on cytogenetic profile of these mahseer species isdiscussed in the light of cytotaxonomic implications and understanding the karyoevolution of thesefish species.