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Taxonomic revision of Phoxinus from the Caucasus revealed two distinct species. One species, P. colchicus , was known from eastern drainage of Black Sea, but was recorded also in the middle reach of the Kuban (Sea of Azov basin), for the first time. The Kuban population represents a genetically unique sub-lineage of P. colchicus . Its ancestors might have colonized the Kuban system through the event of ancient river capture. Another species inhabits only the Adagum River basin in the lower Kuban and represents a new narrow-ranged endemic species – Phoxinus adagumicus sp. nov. According to mtDNA phylogeny (COI and cyt b ), P. adagumicus sp. nov. represents deeply divergent and one of the two early branched lineages of the genus Phoxinus being distant to other species (min. p -distance = 0.074) including geographical neighbors – P. chrysoprasius from Crimean Peninsula and P. colchicus from the Caucasus. The new species differs from most Phoxinus species by frequently occurring single-row pharyngeal teeth (modal formula 5–4). The narrow geographic range (ca. 55 km in length and 15–20 km in width) and high anthropogenic load on local water systems suggests the new species is under threat and needs protection.
Artaev et al. (Wed,) studied this question.