Russian, Kazakh and US scientists jointly confirm: "common minnow" in three Central Asian lakes is actually a separate new genus, Tianshanophoxinus

Russian, Kazakh and American researchers have jointly confirmed that a small cyprinid fish distributed across the basins of three Central Asian lakes—treated for nearly 150 years as the common minnow—actually constitutes a separate ancient evolutionary lineage, and have accordingly described it as a new genus, Tianshanophoxinus. The findings were produced jointly by researchers from the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences (Moscow), the Papanin Institute for Biology of Inland Waters of the Russian Academy of Sciences (Borok), Al-Farabi Kazakh National University and the American Museum of Natural History.

The fish studied closely resembles the minnow—a small freshwater cyprinid. Over the past 150 years, scholars have repeatedly moved it between genera based on external morphological features, placing it successively in the genera Phoxinus, Rhynchocypris and Lagowskiella, but never tested these judgements with genetic methods.

Researchers collected specimens in the basins of Lake Balkhash, Lake Alakol and Lake Issyk-Kul in Kazakhstan and Kyrgyzstan, and studied historical specimens held in the collections of the Zoological Institute of the Russian Academy of Sciences. They analysed 56 morphological characters in 150 fish, took X-rays of the skeleton, and sequenced two mitochondrial genes and two nuclear genes.

The results showed that these fish cannot be assigned to the true genus Phoxinus: their mitochondrial DNA differs from that of their closest relatives by about 11%, a level comparable to the divergence between confirmed genera of cyprinids. The authors therefore propose placing the study subjects in a separate genus, Tianshanophoxinus.

Genetically, the closest relatives of Tianshanophoxinus are the Altai osmans (genus Oreoleuciscus) found in the rivers of Mongolia and the upper Ob River. The two closely related groups differ markedly in appearance: Tianshanophoxinus reaches a body length of only about 10 cm, whereas osmans can grow to nearly 1 m.

The authors also identified morphological features unique to the new genus: most Tianshanophoxinus have almost no lateral line—the sensory organ that runs along the body in many fish; their pectoral and pelvic fins are short, and they have fewer vertebrae than their close relatives.

The new genus contains three species: Tianshanophoxinus poljakowii, Tianshanophoxinus kuldschiensis and Tianshanophoxinus issykkulensis. For two of these species, the authors selected type specimens from old collections to fix their scientific names.

According to the authors' hypothesis, the ancestors of the new fish entered the ancient Balkhash-Alakol water body from the Irtysh River basin via the Junggar Basin; this water body repeatedly expanded and broke up into isolated water bodies during glacial and interglacial periods, and these fluctuations separated populations into different species; later, during periods of rising water levels, the fish spread westward along the Chu River and entered Lake Issyk-Kul. Today, Tianshanophoxinus often inhabits groundwater seepage sites—springs and streams overgrown with aquatic vegetation—which may have served as refuges for them during climate change.

"We are used to genetics revealing sibling species that look almost identical, but here a familiar name concealed a full century and a half of independent evolution—a separate genus. This shows that even in regions considered well studied, we have underestimated fish diversity," said Boris Levin, chief researcher at the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences and Candidate of Biological Sciences.

The researchers note that this important discovery in the field of biodiversity also matters for nature conservation. The species of the new genus mainly inhabit small ecosystems, and these water bodies are being affected by irrigation withdrawals, pollution, the introduction of alien species and increasing climate aridity; Lake Issyk-Kul is also under growing pressure from tourism and construction development. The institute's press service stressed: "When this group was regarded as part of the widely distributed minnow, its vulnerability was underestimated. It is now clear that an entire evolutionary line may be under threat."