Cobitis derzhavini sp. nova-a New Spined Loach Species (Teleostei: Cobitidae) Discovered in the Transcaucasia

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 3/4 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).