Squalius, Bonaparte, 1837

Freyhof, JÖrg, Yoğurtçuoğlu, Baran, Jouladeh-Roudbar, Arash & Kaya, Cüneyt, 2025, Handbook of Freshwater Fishes of West Asia, De Gruyter : 399-401

Squalius

Chubs are medium-sized to large fishes that inhabit lakes, slow-flowing large rivers, and hill streams. In this genus, 38 species are recognised, 16 of which are found in West Asia. They are particularly abundant in medium-sized streams and small rivers with gravel substrate and may constitute a significant portion of the fish biomass in such habitats. Squalius is characterised by scaled midventral keel in front of the anus, a complete lateral line, a slightly subterminal mouth, the dorsal origin behind the pelvic base, two rows of pharyngeal teeth, the absence of a prominent grey or brown lateral stripe (a very indistinct stripe is present in a few species), 7–10½ branched anal rays and 7–9½ branched dorsal rays. In Anatolia, mtDNA studies have only partially corroborated the morphological species hypothesis in recent years. This is due to several factors, including intro- gressive hybridisation and the possibility that some species may have arisen through genetic drift in small founder pop- ulations invading new habitats. Genetic drift is a potential evolutionary pathway of S. carinus , which has a very small range adjacent to its closely related sister species. Addition- ally, some species have been identified as synonyms due to underestimating their morphological variability. The

species diversity of Squalius is still incompletely understood and future studies of nuclear DNA may change the species diversity recognised here. In Anatolia, Eastern Greece, and Bulgaria, one very widespread molecular group is distrib- uted, having the mtDNA of S. orpheus . However, nuclear DNA data strongly suggest that Greek and Anatolian pop- ulations are two species: S. orpheus and S. cappadocicus . Indeed, selected populations are quite different from each other and there are plenty of intermediate populations, making separating species impossible for now. An additional complex situation is found in the Persian Gulf basin, where S. lepidus , S. berak , and S. verepi often share the same mtDNA sequences. They seem also to have often hybridised and such hybrids have locally stabilised, and populations are being morphologically intermediate between S. berak /S. verepi and S. lepidus , challenging their identification. In other populations, the external appearance of the fish is identical to that of one species, yet the mitochondrial DNA (mtDNA) belongs to the different species. Genomic studies will shed some light on Squalius ’ evolutionary past, hopefully soon.

Further reading. Durand et al. 2000 (molecular diversity); Özuluğ & Freyhof 2011 (morphological diversity in Western Anatolia).

Keys to species of Squalius in West Asia

Contributing author: Esra Bayçelebi ( Rize) contributed to the chapter on the genus Squalius .

Black and Marmara Sea basins

1a - Vertical black bar behind opercle conspicuous; anal rays and membranes orange or red in life in adults larger than 150 mm SL. ……………… S. orientalis

1b - Vertical black bar behind opercle in-conspicuous; anal membranes whitish, yellowish, very pale-orange-grey or blackish, rays usually blackish in life in adults larger than 150 mm SL. ………………2

2a - 47–49 total lateral-line scales; head length 24–26 % SL. ……………… S. cii

2b - 40–46 total lateral-line scales; head length 25–29 % SL. ………………3

3a - Dorsal origin situated behind of pelvic base; posteriormost point of anal at tip of 7 th or 8 th branched ray. ……………… S. pursakensis

3b - Dorsal origin situated above pelvic base; posteriormost point of anal at tip of 3 rd –5 th branched ray ……………… S. cappadocicus

Central Anatolian endorheic basins, Aegean and Mediterranean basins east to Bay of Antalya

1a - 14–15 circumpeduncular scales; scale pockets on flank with a dark-grey, crescent-shaped mark. ………………2

1b - 16–18 circumpeduncular scales; scale pockets on flank with a dark-brown or grey spot or roundish blotch on middle of flank scale. ………………4

2a - Lower lip clearly projecting beyond upper lip; usually 9½ anal rays. ……………… S. anatolicus

2b - Upper lip clearly projecting beyond lower lip or both lips at equal level; 7–8½, very rarely 9½ anal rays. ………………3

3a - Dorsal origin situated behind of pelvic base; posteriormost point of anal at tip of 7th or 8th branched ray. ……………… S. pursakensis

3b - Dorsal origin situated above pelvic base; posteriormost point of anal at tip of 3th–5th branched ray ……………… S. cappadocicus

4a - A conspicuous broad, dark-brown stripe on upper part of flank between head and end of caudal peduncle; 37–40+2–3 lateral-line scales. ……………… S. kosswigi

4b - No stripe on flank; 40–43+2–3 lateral-line scales. ………………5

5a - Dark-brown in life; lower lip projecting beyond tip of upper lip (equal to tip of upper lip in few individuals); upper head profile straight; snout conical and pointed; interorbital area straight or slightly convex. ……………… S. carinus

5b - Silvery or golden in life; upper lip projecting beyond tip of lower lip or mouth terminal; upper head profile convex; snout rounded with obtuse tip; interorbital area convex. ………………6

6a - Mouth subterminal in adults; dorso-hypural distance reaching nostrils, rarely to anterior half of eye when reported forwards. ……………… S. fellowesii

6b - Mouth terminal or slightly subterminal in adults; dorso-hypural distance reaching anterior half of eye when reported forwards. ……………… S. aristotelis

Eastern Mediterranean (Seyhan, Ceyhan, Orontes)

1a - Lower lip projecting beyond upper lip; 9–10½ branched anal rays. ……………… S. kottelati

1b - Upper lip projecting beyond lower lip or tip of both lips equal; 7–8½ branched anal rays. ……………… S. cappadocicus

Persian Gulf, Caspian, Lake Namak, Western Kavir, and Lake Urmia basins

1a - Mouth superior in adults; 9–10½, rarely 8½ branched anal rays; posterior anal margin straight. ……………… S. lepidus

1b - Mouth terminal or subterminal in adults; (7½) 8½, very rarely 9 ½ branched anal rays, posterior anal margin convex. ………………2

2a - Knob on lower jaw symphysis wide, thick; anal rays orange. ……………… S. namak

2b - Knob on lower jaw symphysis narrow, thin, or absent; anal rays hyaline, grey or black, orange in some individuals and populations. ………………3

3a - Anal with numerous black pigments on rays in preserved individuals; 11–12 gill rakers; anal height 14–18 % SL. ……………… S. cappadocicus

3b - Anal with few or without black pigments in preserved individuals; 7–11 gill rakers; anal height 17–27 % SL. ………………4

4a - Head length 27–32 % SL. ……………… S. berak / S. verepi

4b - Head length 24–28 % SL. ………………5

5a - Posteriormost point of anal at tip of 5th or 6th branched ray. ……………… S. turcicus

5b - Posteriormost point of anal at tip of 3rd or 5th branched ray. ……………… S. agdamicus