The karyotype of the Amu Darya sturgeon, Pseudoscaphirhynchus kaufmanni (Actinopterygii: Acipenseriformes: Acipenseridae)

Abstract

Background. Karyological studies of acipenserid fishes are of great importance because they present the only direct method to evaluate their ploidy levels for further research on polyploid evolution in these fishes. They are also important for prediction of the results of interspecific hybridizations in sturgeon aquaculture. None of the species of the genus Pseudoscaphirhynchus has hitherto been studied karyologically. The aim of this paper was to present the first data on the karyotype of the dwarf form of Pseudoscaphirhynchus kaufmanni (Kessler, 1877). Materials and methods. Three females of the dwarf form of Pseudoscaphirhynchus kaufmanni of the total body length 19–23 cm were caught in the Vakhsh River (Amu Darya River drainage), Tadzhikistan, in 2012. The chromosome slides were prepared by using previously published karyological method of Vasil’ev and Sokolov. Totally, 14 metaphase plates were analyzed. Results. The karyotype of Pseudoscaphirhynchus kaufmanni consists of 118–120 chromosomes and includes about 18–20 large bi-armed chromosomes, about 32–34 small bi-armed chromosomes, from one to two pairs of large acrocentrics, and about 64 small acrocentrics or microchromosomes. Conclusion. The karyological study revealed that Pseudoscaphirhynchus kaufmanni belongs to low-chromosome acipenserid group with about 120 chromosomes. Its karyotype demonstrates noticeable differences from the karyotype of the shovelnose sturgeon, Scaphirhynchus platorhynchus (Rafinesque, 1820), in the number of large acrocentrics, thereby, karyological data confirms polyphyletic origin of the subfamily Scaphirhynchinae (or tribe Scaphirhynchini).

Keywords

• acipenserids
• karyology
• ploidy levels
• polyphyly