Phoxinus ayukensis, Artaev & Turbanov & Bolotovskiy & Gandlin & Levin, 2025

Artaev, Oleg N., Turbanov, Ilya S., Bolotovskiy, Aleksey A., Gandlin, Alexander A. & Levin, Boris A., 2025, A new super narrow-ranged endemic Phoxinus minnow (Leuciscidae) from the Caucasus, Zoosystematics and Evolution 101 (3), pp. 1137-1154 : 1137-1154

Phoxinus ayukensis sp. nov.

Figs 2 , 3 , 8 English name: Ayuk minnow Russian name: Аюкский гольян

Phoxinus phoxinus – Sukhanova and Troitskiy 1949: 154, 164–165 (part., upstream of Ayuk River); Emtyl et al. 1994: 137–141, figs 1, 2 (part., Ayuk River); Reshetnikov et al. 2003: 301–302 (part., Kuban River).

Phoxinus phoxinus kubanicum Emtyl & Ivanenko, 2002, unavailable name: 90–92, fig. 69 ex Berg 1949, not P. adagumicus and P. ayukensis sp. nov. (part., Psekups River basin); Otrishko and Emtyl 2013 a: 20 (part., Kuban basin).

Phoxinus kubanicus [sic] – Otrishko and Emtyl 2013 b: 69 –70 (part., Ayuk River).

Type material.

Holotype, • IBIW_FS_501 , female (54.3 mm SL, GenBank accession numbers PQ 998252 – COI, PV 105509 – cyt b), Russia, Krasnodar Krai, Kuban River drainage, Ayuk (= Burlachenkova Shchel, Peshchernaya Shchel, Semenovskaya Shchel) Stream, tributary of Chepsi River, upstream Fanagoriyskoe Vil. , 44.4756°N, 39.0196°E, 19 July 2024, O. N. Artaev leg. Paratypes: • 3 females, 1 male ( IBIW_FS_502 ), SL 37.5–54.8 mm ; • 2 females, 1 male ( ZISP 57075 ), SL 39.3–50.2 mm ; • 3 females ( ZMMU P-24653 ), SL 38.6–50.0 mm, all from the same locality and date as holotype .

Additional material.

Suppl. material 6.

Comparative material.

Suppl. material 6.

Material used in genetics.

Suppl. material 4.

Diagnosis.

Phoxinus ayukensis sp. nov. is distinguished from other European and circum-Black Sea Phoxinus species ( P. abanticus , P. adagumicus , P. bigerri , P. chrysoprasius , P. colchicus , P. csikii (Clade 5), P. dragarum , P. fayollarum , P. isetensis , P. karsticus , P. krkae , P. lumaireul (Clade 1 b, 1 a), P. marsilii (Clade 9), P. radeki , P. septimaniae , and P. strandjae Drensky, 1926 ) by increased number of scales in the lateral series 87–105 (mean 97.7); from species from Eastern Europe and the Caucasus ( P. adagumicus , P. chrysoprasius , P. colchicus and P. isetensis ) by increased frequency of occurrence of seven rays in the pelvic fin (ca. 35 %) and increased numbers of scales between first unbranched rays of dorsal and anal fins (32–41, mean 36.7).

Description.

The live and preserved appearance as well as radiograph of holotype is shown on Fig. 2 , general appearance of live female and male of Phoxinus ayukensis sp. nov. from type locality is shown on Fig. 3 , morphometrics of holotype, paratypes and additional material from the type locality with level of significance of sex-related differences are given in Table 2 , meristic and qualitative characters for specimens from type locality are given in Table 3 , primary morphological data for specimens from the type locality (holotype, paratypes and additional material) are given in Suppl. material 1, morphometrics of P. ayukensis sp. nov., P. isetensis , P. adagumicus , P. chrysoprasius and P. colchicus with their comparison are given in Suppl. material 2, meristic and qualitative characters of P. ayukensis sp. nov. and other Phoxinus spp. are given in Suppl. material 3.

Morphometrics (Table 2 , Suppl. materials 1, 2). The new species has a rather small size — the maximum SL is 54.8 mm. The new species has eye horizontal diameter 7.0 % HL in holotype, 7.0–8.7 % in paratypes and additional material from type locality; caudal peduncle width 7.9 % SL in holotype, 7.0–8.4 % in paratypes and additional material from type locality; head length 145.2 % body depth in holotype, 120.2–152.9 % in paratypes and additional material from type locality.

Meristics (Table 3 , Suppl. material 3). Dorsal fin with 3 unbranched and 7 ½ branched rays. Anal fin with 3 unbranched and 7 ½ branched rays. Pectoral fin with 14–16 rays, often 15–16. Pelvic fins with 7–8 rays. Caudal fin with 19 rays (rarely 18 and 20 rays). Number of dorsal procurrent caudal-fin rays 10–13. Number of ventral procurrent caudal-fin rays 6–10. Pharyngeal teeth are two-rowed, with the common formula 2.5–4.2. However, appr. 30 % of individuals exhibit a reduction of the second row to a single tooth, at least on one pharyngeal bone. Total number of vertebrae in the holotype 40, 39–41 in the paratypes, and in the add. material, commonly 40. Number of abdominal vertebrae in the holotype 22, 21–23 in the paratypes, and 21–24 in the add. material, commonly 22 or 23. Number of caudal vertebrae in the holotype 18, 17–19 in the paratypes, and 16–19 in add. material, commonly 17 and 18. Number of predorsal abdominal vertebrae in the holotype 14, 14–15 in the paratypes, and in the add. material, commonly 14 or 15. Number of anal-fin pterygiophores in front of the first caudal vertebrae in the holotype 5, 4–7 in the paratypes, and in the add. material, commonly 5 or 6. Difference in the number of abdominal and caudal vertebrae in the holotype 4, 2–6 in the paratypes, and 2–8 in the add. material, commonly 4–6.

Lateral line incomplete and discontinuous. Total number of scales in the lateral line series 87–105, mean 97.7. Total number of lateral-line (pored) scales 9–54, mean 30.5. Number of scales between bases of dorsal and anal fins 32–41, mean 36.7. Number of circumpeduncular scales 41–49, mean 45.1.

Gill rakers on the first left gill arch 7–9, mean 7.9.

Qualitative characters. Free margin of the dorsal fin is mainly slightly convex, rarely straight; anal fin most often slightly convex, rarely straight or slightly concave. Origin of anal fin in half the cases at the level of posterior insertion of the dorsal fin, often slightly ahead, rarely slightly behind. Third-fourth type of breast scalation with a predominance of fourth type.

Coloration. Outside the spawning period, males and females are olive-yellow-green in color with very little contrast between horizontal zones and vertical stripes. In general, females have less and males have more saturated coloration. The horizontal stripe along the back of the body is practically not expressed in adults and weakly expressed in juveniles.

Sexual dimorphism. There are significant differences in 7 out of 41 morphometric characters (Table 2 ). In addition to classical sex characteristics in Phoxinus minnows (narrower pectoral fins and less bright colors in females), females have a lower head depth at nape relative to the length of the head and body and greater pectoral – pelvic-fin origin length.

Etymology.

The new species is named after the Ayuk (= Burlachenkova Shchel, Peshchernaya Shchel, Semenovskaya Shchel) Stream – the only known habitat area. Name of the Ayuk Stream apparently comes from the Adyghe language word “ ayuko ”, which means “ unfriendly valley ”. Ayukensis – an adjective.

Taxonomic remarks.

Taxonomic affiliation of Phoxinus minnows from the Ayuk Stream, along with minnows from the lower Kuban basin, which were recently described as a separate species ( Artaev et al. 2024 a), was questionable and was cautiously attributed to both P. phoxinus (Sukhanova and Troitsky 1949) and Phoxinus phoxinus kubanicum [sic] ( Otrishko and Emtyl 2013 a) and Phoxinus kubanicus [sic] ( Otrishko and Emtyl 2013 b). The latter two cannot be considered as available names ( Bogutskaya et al. 2023, Artaev et al. 2024 a). Also, based on a discriminant analysis of the external morphological characteristics of minnows from the Ayuk Stream and Durso River (the latter is inhabited by P. colchicus ), it was proposed that minnows from the Ayuk Stream “ attributed to the subspecies of Colchis minnow ” ( Emtyl et al. 1994). However, these assumptions were based on insufficient data and cannot be considered taxonomically valid.

Type locality.

Ayuk (= Burlachenkova Shchel, Peshchernaya Shchel, Semenovskaya Shchel) Stream (44.4756°N, 39.0196°E) upstream of Fanagoriyskoe Vil., Krasnodar Krai, Russia (Fig. 4 ). A tributary of the Chepsi River → Psekups River → Kuban River (Krasnodar Reservoir) → Sea of Azov.

Distribution and habitats.

New species has an extremely narrow range and is known from the Ayuk Stream only in the area of the Ayuk waterfalls and above them (Fig. 4 ). The total length of the river is about 12 km, the upper stream of which (5–7 km) is inhabited by the core population. Some individuals occasionally migrate downstream to the confluence with the Chepsi River (about 5.5 km) (Fig. 5 ). In the summer, the water level is low, surface runoff stops, and water pools remain in the deep parts of the riverbed, which are apparently supplied by interstitial waters (Fig. 4 A ). Such water pools are inhabited by P. ayukensis sp. nov. only.

Morphological comparisons.

Cluster analysis of the mean values of 41 morphometric characters for five geographically close species demonstrates that Phoxinus ayukensis sp. nov. is the most distinct, not only from the closely related and neighboring P. adagumicus but also from other Crimean and Caucasian species, and is most similar to the northwardly distributed P. isetensis (Fig. 6 A ). The discriminant function analysis of eight external meristic characters effectively differentiates the new species from the other four species under comparison (Fig. 6 B ): DFA statistics values are as follows: Wilks’ λ = 0.03094, approx. F (56.103) = 16.74, p <0.0000. The PCA analysis of eight meristic traits has also demonstrated clear separation of the new species (Fig. 7 ). Notably, the characters contributing to the separation of new species are related to the body squamation: cps, bda, and sql.

The new species differs from the other European Phoxinus species by a significantly increased number of scales in the lateral series (Table 4 ). The increased squamation of the new species is also characteristic of the number of scales between the bases of the dorsal and anal fins. Another feature that distinguishes the new species from the six other studied species is the high frequency of reduction of the total number of rays to 7 in the pelvic fins observed in each third specimen (Fig. 8 D ).

Compared to Phoxinus abanticus from the Lake Abant basin in Türkiye ( Turan et al. 2023), P. ayukensis sp. nov. has a lower body – body depth 17.0–21.8 % SL (vs. 22–25 %); 87–105 total number of scales in lateral series (vs. 60–69); 19–23 scales above lateral line (vs. 11–14); 13–18 scales below lateral line (vs. 7–10); scales on breast patches in males (vs. no scales in males).

Compared to Phoxinus adagumicus from another part of the Kuban system, Adagum River basin, Russia ( Artaev et al. 2024 a), P. ayukensis sp. nov. has larger eye horizontal diameter 27.5–32.5 %, mean 29.9 % HL (vs. 22.9–28.5 %, mean 25.9 %) in females and 24.5–30.9 %, mean 28.9 % HL (vs. 21.8–25.9 %, mean 24.5 %) in males; 87–105, mean 97.7 total number of scales in lateral series (vs. 74–94, mean 84.5); 32–41, mean 36.7 scales between bases of dorsal and anal fins (vs. 26–36, mean 31.2); 13–18, mean 15.3 scales below lateral line (vs. 8–14, mean 11.8); 4–7, mean 5.7 number of anal-fin pterygiophores in front of the first caudal vertebrae (vs. 3–7, mean 4.4); 7–8, mean 7.6 rays in pelvic fins (vs. 7–9, mean 8.0); absence of single-row pharyngeal teeth (vs. dominance) and the predominance of the classical dental formula for the genus - 2.5–4.2 (vs. predominance 5-4) (Suppl. materials 2, 3).

Compared to Phoxinus bigerri from the Adour and the Leyre drainages in France ( Denys et al. 2020), P. ayukensis sp. nov. has 87–105 total number of scales in lateral series (vs. 68–87). Compared to P. bigerri from Estuary of Bilbao in Spain ( Palandačić et al. 2024) has 87–105, mean 97.7 total number of scales in lateral series (vs. ca. 66–85, mean 76.6); 9–54, mean 30.5 numbers of lateral-line scales (pored) (vs. ca. 31–80, mean 66.0); 3 rd – 4 th types of scalation pattern of the breast and anterior belly with predominance of 4 th type (vs. 3 rd – 7 th, 9 th, 11 th, and 12 th types with predominance of 3 rd type) (Suppl. material 3).

Compared to Phoxinus chrysoprasius from the rivers of the Crimean Peninsula ( Bogutskaya et al. 2023; Artaev et al. 2024 a), P. ayukensis sp. nov. has larger eye horizontal diameter 27.5–32.5 %, mean 29.9 % HL (vs. 18.5–26.0 %, mean 23.5 %) in females; 87–105, mean 97.7 total number of scales in lateral series (vs. 78–104, mean 89.9); 7–8, mean 7.6 rays in pelvic fins (vs. 7–9, mean 8.0); 14–16, mean 15.4 rays in pectoral fins (vs. 13–19, mean 17.0); 9–54, mean 30.5 lateral-line (pored) scales (vs. 46 – ca. 100, mean 72.8) (Suppl. materials 2, 3).

Compared to Phoxinus colchicus from the Kuban basin and rivers of the Black Sea coast of the Caucasus ( Artaev et al. 2024 a), P. ayukensis sp. nov. has larger head length 130.9–152.9 %, mean 142.9 % to body depth (vs. 97.4–129.8 %, mean 111.6 %) in females and 120.2–151.6 %, mean 140.2 % (vs. 106.6–139.1 %, mean 120.9 %) in males; 87–105, mean 97.7 total number of scales in lateral series (vs. 76–96, mean 82.9); 5–7, mean 6.4 number of scale rows on left and right breast patches (vs. 5–10, mean 8.0); 41–49, mean 45.1 circumpeduncular scales (vs. 36–48, mean 40.9); 32–41, mean 36.7 scales between bases of dorsal and anal fins (vs. 30–37, mean 33.0); 3 rd – 4 th types of scalation pattern of the breast and anterior belly with predominance of 4 th type (vs. 3 rd – 10 th, 13 th, and 14 th types with predominance of 6 th type); 7–8, mean 7.6 rays in pelvic fins (vs. 8–9, mean 8.1) (Suppl. materials 2, 3).

Compared to Phoxinus csikii from the Danube River basin, Montenegro, and Bulgaria ( Bogutskaya et al. 2019, 2023), P. ayukensis sp. nov. has 87–105, mean 97.7 total number of scales in lateral series (vs. ca. 71–100, mean 84.8); 9–54, mean 30.5 lateral-line (pored) scales (vs. ca. 11–80, mean 52.9); 3 rd – 4 th types of scalation pattern of the breast and anterior belly with predominance of 4 th type (vs. 3 rd – 9 th and 11 th types with predominance of 7 th type) (Suppl. material 3).

Compared to Phoxinus dragarum from the Garonne drainage in France ( Denys et al. 2020), P. ayukensis sp. nov. has 87–105 total number of scales in lateral series (vs. 70–97); 9–54 lateral-line (pored) scales (vs. 50–74).

Compared to Phoxinus fayollarum from the Loire drainage in France ( Denys et al. 2020), P. ayukensis sp. nov. has 87–105 total number of scales in lateral series (vs. 72–91); 9–54 lateral-line (pored) scales (vs. 56–84).

Compared to Phoxinus isetensis from basins of Baltic, Barents, Caspian Seas and Kara Sea basin ( Artaev et al. 2024 b), P. ayukensis sp. nov. has 87–105, mean 97.7 total number of scales in lateral series (vs. 71–103, mean 85.7); 9–54, mean 30.5 lateral-line (pored) scales (vs. 23–66, mean 50.8); 41–49, mean 45.1 circumpeduncular scales (vs. 33–39, mean 35.2); 19–23, mean 21.1 scales above lateral line (vs. 14–18, mean 15.4); 13–18, mean 15.3 scales below lateral line (vs. 9–14, mean 11.4); 32–41, mean 36.7 scales between bases of dorsal and anal fins (vs. 22–35, mean 27.7); 7–8, mean 7.6 rays in pelvic fins (vs. 7–9, mean 8.0); 39–41, mean 40.0 total number of vertebrae (vs. 39–42, mean 41.0); 16–19, mean 17.3 caudal vertebrae (vs. 16–21, mean 18.9); difference between numbers of abdominal and caudal vertebrae is 2–8, mean 5.3 (vs. 0–7, mean 3.2) (Suppl. material 3).

Compared to Phoxinus karsticus from Lake Skadar ( Palandačić et al. 2024), P. ayukensis sp. nov. has 97.7 mean number of total number of scales in lateral series (ca. 76–90, mean vs. 80.4); 3 rd – 4 th types of scalation pattern of the breast and anterior belly with predominance of 4 th type (vs. 3 rd – 7 th, 9 th types with predominance of 3 rd type).

Compared to Phoxinus krkae from the Krka River, Croatia ( Bogutskaya et al. 2019), P. ayukensis sp. nov. has 87–105, mean 97.7 total number of scales in lateral series (vs. 72–84, mean 78.5); 3 rd – 4 th types of scalation pattern of the breast and anterior belly with predominance of 4 th type (vs. 3 rd – 7 th types with predominance of 6 th type); 39–41, mean 40.0 total number of vertebrae (vs. 37–40, mean 38.4); 21–24, mean 22.8 abdominal vertebrae (vs. 21–22, mean 21.6) (Suppl. material 3).

Compared to Phoxinus lumaireul clades 1 a and 1 b from the rivers in the Adriatic and Black Sea basins in Italy, Slovenia, and Croatia ( Bogutskaya et al. 2019), P. ayukensis sp. nov. has 87–105, mean 97.7 total number of scales in lateral series (vs. ca. 71–105, mean 82.3); 3 rd – 4 th types of scalation pattern of the breast and anterior belly with predominance of 4 th type (vs. 2 nd – 7 th types with predominance of 3 rd type) (Suppl. material 3).

Compared to Phoxinus marsilii from the Danube River basin, Austria and Croatia ( Bogutskaya et al. 2019, 2023), P. ayukensis sp. nov. has 87–105, mean 97.7 total number of scales in lateral series (vs. ca. 71–95, mean 84.0); 9–54, mean 30.5 lateral-line (pored) scales (vs. ca. 11–90, mean 65.4); 3 rd – 4 th types of scalation pattern of the breast and anterior belly with predominance of 4 th type (vs. 3 rd – 8 th types with predominance of 6 th type); 21–24, mean 22.8 abdominal vertebrae (vs. 20–23, mean 21.8); difference between numbers of abdominal and caudal vertebrae is 2–8, mean 5.3 (vs. 1–6, mean 3.0) (Suppl. material 3).

Compared to Phoxinus phoxinus from France ( Denys et al. 2020), P. ayukensis sp. nov. has an almost non-overlapping caudal peduncle depth 2.1–2.8 times its length (vs. 2.8–3.9).

Compared to Phoxinus radeki from the Ergene River (Aegean Sea basin) in Türkiye ( Bayçelebi et al. 2024), P. ayukensis sp. nov. has 87–105 total number of scales in lateral series (vs. 75–96); 19–23 scales above lateral line (vs. 9–15); 13–18 scales below lateral line (vs. 6–9); 14–16 rays in pectoral fins (vs. 16–18).

Compared to Phoxinus septimaniae from the Herault River, France ( Bogutskaya et al. 2019), P. ayukensis sp. nov. has 87–105, mean 97.7 total number of scales in lateral series (vs. ca. 81–90, mean 85.6 or 75–94 ( Denys et al. 2020)); 3 rd – 4 th types of scalation pattern of the breast and anterior belly with predominance of 4 th type (vs. 12 th – 14 th types with predominance of 14 th type); 21–24, mean 22.8 abdominal vertebrae (vs. 21–23, mean 21.8) (Suppl. material 3).

Compared to Phoxinus strandjae from the rivers of the Black Sea basin, Bulgaria, and the rivers of the Marmara Sea, Türkiye ( Bogutskaya et al. 2019, 2023), P. ayukensis sp. nov. has 87–105, mean 97.7 total number of scales in lateral series (vs. ca. 76–100, mean 88.3); 3 rd – 4 th types of scalation pattern of the breast and anterior belly with predominance of 4 th type (vs. 3 rd – 12 th types with predominance of 6 th, 7 th, 9 th, and 11 th types) (Suppl. material 3).

Figures

Figure 2. Holotype of Phoxinus ayukensis sp. nov. (SL 54.3 mm, IBIW _ FS _ 501, female). A. Live appearance; B. General appearance of the preserved specimen; C. Radiograph.

Figure 3. Live coloration of female and male of Phoxinus ayukensis sp. nov. (paratypes, IBIW _ FS _ 502) from type locality (Ayuk Stream) and P. adagumicus, another congeneric species inhabiting the Kuban River basin (female with eggs; 44.4960 ° N, 38.4330 ° E; 8 May 2022; IBIW _ FS _ 338) from Zybza River. Side and ventral views are of the same specimens. Photo by Oleg Artaev.

Figure 4. Habitat of Phoxinus ayukensis sp. nov.: A. Puddle in the bed of Ayuk Stream, sampling place of the type material (44.4756 ° N, 39.0194 ° E, 19 July 2024, photograph by Oleg Artaev); B. One of a series of waterfalls that restrict the distribution of P. ayukensis sp. nov. (44.4749 ° N, 39.0209 ° E, 9 March 2025, photograph by Andrey Ostapenko).

Figure 5. Map of Phoxinus species distribution in the Northwestern Caucasus (based on own data).

Figure 6. Dendrograms (UPGMA): A. Average values of 41 morphometric characters for each species with bootstrap support on each node (Euclidean distance); B. Eight external meristic characters based on squared Mahalanobis distances defined by discriminant functions in DFA. In both cases, the difference was statistically significant between all species compared (p < 0.005). A schematic map of species ranges in the center, with colors corresponding to the species names.

Figure 7. PCA of Phoxinus spp. based on eight meristic characters and loading plot showing how strongly each character influences principal components.

Figure 8. Some morphological features of Phoxinus ayukensis sp. nov. A. Example of squamation of middle part of body of an alizarin-stained specimen (colors changed): a diagonal line marks the direction of scale counting between first unbranched rays of dorsal and anal fins (bda), above (all) and below (bll) lateral line (bda = 36, all = 21, and bll = 14 scales); B. Ventral view of pelvic fins, genital and anal openings in females and males; C. Dentition of pharyngeal bones: double-row formula 1.5–4.1 (observed in 10 % of specimens); D. Ventral view of an alizarin-stained specimen showing 3 rd-type scalation on the breast and belly and reduction of ray numbers to seven in both pelvic fins. Scale bar: 0.5 mm (C).