A species of fish new to science, discovered in the water bodies of the North Caucasus, turns out to be an endemic relic with a narrow areas

Fig.1. Photographs of a living Phoxinus adagumicus

The species diversity of fish in continental reservoirs and watercourses is significantly underestimated. As a team of scientists from the A.N. Severtsov Institute of Ecology and Evolution RAS and the I.D. Papanin Institute of Biology of Inland Waters RAS have found out, the species richness of fish in Russian water bodies is also underestimated. In particular, while conducting an audit of small carp fish - minnows of the genus Phoxinus, living in the North Caucasus, scientists discovered that two species of minnows inhabit it. One of the species is the Colchian minnow Phoxinus colchicus, widespread in the rivers of the eastern Black Sea basin, and the second is a new species for science that lives in the rivers of the Adagum system, a tributary of the lower Kuban (Fig. 3). The latter is named the Adagum minnow Phoxinus adagumicus (Fig. 1).

Fig.2. Reduced pharyngeal teeth of the Adagum minnow: A) single row 5-4 (in 33% of individuals), B) double row – 1.5-4.1 (21% of individuals).

The species, new to science, differs from other species of the genus, first of all, in its reduced pharyngeal teeth (Fig. 2) and a number of other characteristics. According to molecular genetic analysis of two mtDNA markers, the new species represents one of the most ancient lineages of Phoxinus in Europe and among the first to penetrate from the Far East in the distant past (Fig. 4). In fact, this is a relict line of minnows that has survived to this day in the lower reaches of the Kuban.

Fig.3. Map of collections of materials and distribution of a new species of fish - the Adagum minnow.

It turned out that the Colchian minnow also lives in the Kuban basin, having penetrated into the basin of the Belaya River, the largest tributary of the Kuban. A population of Colchis minnow with a unique haplogroup and a fairly high level of genetic isolation from Colchis minnows of the Black Sea basin was discovered here. This speaks in favor of an ancient event of river interception between the Kuban basin and the Black Sea rivers.

Fig.4. Bayesian consensus tree of concatenated mtDNA protein-coding sequences (COI and cytb) representing the relationships of all species of the genus Phoxinus.

Kuban is a river with the highest endemism of ichthyofauna among the rivers of European Russia. As the study showed, the extent of endemism in Kuban is still underestimated.

The species, new to science, has a very small range, limited to dimensions of about 55 x 20 km in the Adagum basin (Lower Kuban). The habitat of the Adagum minnow is located in a region of intense anthropogenic pressure. Obviously, this endemic species requires conservation measures.

The article was published in the journal Zoosystematics and Evolution (Q1 WoS).

The work was supported by the Russian Science Foundation grant No. 23-14-00128.