The study of spined loaches from the southwestern Caspian Sea basin revealed one new species. Cobitis derzhavini sp. nova is described from the lower Kura River drainage in the Ganja-Qazakh region of Azerbaijan. It is distinguished from the most of its congeners distributed in the Caucasus and in the Caspian Sea basin (C. saniae, C. faridpaki, C. satunini, and C. taenia) by the absence of an obvious dark spot at the uppermost caudal-fin base, as well as by a combination of other morphological features, none of them unique. In the Agstafa River Cobitis derzhavini sp. nova is found sympatrically distributed with C. saniae, its closest relatives in our molecular dataset. These species form separate phylogenetic lineages with high support (PP 0.9 for COI and 1.0 for RAG1). In addition, their reproductive isolation is confirmed by the karyological differences: C. derzhavini sp. nova has 8 meta- and 12 submetacentric chromosomes in its karyotype against 6 meta- and 14 submetacentric chromosomes in C. saniae. Besides the dark spot at the uppermost caudal-fin base developed in the C. saniae, C. derzhavini sp. nova differs from this species by having the plate of lamina circularis reaching in front of ¾ of the third segment of the attached ray, blotches in Z4 smaller than eye diameter, shallow adipose crests on the caudal peduncle, and a shorter caudal peduncle (10–14% SL).

The karyology of species of sturgeon from the Russian Far East demonstrates that the karyotype of the Sakhalin sturgeon (Acipenser mikadoi) includes 262 ± 4 chromosomes with 80 biarmed chromosomes and the number of chromosome arms (NF) 342 ± 4, the karyotype of the Amur sturgeon (A. schrenckii) includes 266 ± 4 chromosomes with 92 biarmed chromosomes and NF 358 ± 4, and the karyotype of the kaluga (A. dauricus) consists of 268 ± 4 chromosomes with 100 biarmed chromosomes and NF 368 ± 4. These results prove that all western Pacific sturgeon species are from a tetraploid origin, based on a recent ploidy scale. This suggests that at least three polyploidization events have occurred during the evolution of Acipenseridae. However, if polyploid species originated by hybridization between diploid species, there may have been more polyploidization events in this group of fishes.