Chondrostoma regium

Common name. Mesopotamian nase.

Diagnosis. Distinguished from other species of Chondrostoma in Caspian, Persian Gulf, and Kor endorheic basin in Iran by: ○ 47−74, usually 58–72, total lateral-line scales / ○ usually 6−6, 7–6 or 7–7 pharyngeal teeth, rarely 6–5 or 7–5 / ○ 8−9½, rarely 7½ or 10½, branched dorsal rays / ○ 8−12½, usually 9−10½, branched anal rays / ○ 22−34 gill rakers / ○ mouth cleft straight or slightly arched / ○ thick cornified sheath covering lower lip / ○ no keel on back in front of dorsal / ○ 45−48, usually 46−47 (27+20, 26+21, 26+20), total vertebrae. Size up to 400 mm SL.

Distribution . Qweiq, Euphrates, Tigris, and Karun drainages. In Zohreh drainage and Kor, Esfahan and Sirjan basins in Iran.

Habitat. Medium-sized streams and springs to large rivers with rocky or gravelly bottoms and swift to moderate currents. Spawns on gravel substrate in fast-flowing stretches of river. In reservoirs, from which they migrate to rivers or streams to spawn.

Biology. Live up to 8 years. First reproduction at 2–4 years and about 130 (males) and 150 (females) mm SL. Spawning season strongly related to altitude and latitude and triggered by water temperature of 15–25°C. Reported to spawn in January (Sirvan, Iraq), March–May (Baghdad, Iraq; Gamasiyab, Iran), May–June (Syria), and April–May in Atatürk reservoir (Türkiye). Feeds on periphyton in rivers, often taking large quantities of plankton in reservoirs.

Conservation status. LC; extirpated from Qweiq. Very rare in Kor, recorded only from Band-e Amir and Ghadamgah spring since 2007.

Remarks. There is one record from the Orontes drainage at Gis as-Sugur in Syria (caught in 1979), but this is doubtful. Chondrostoma orientale from the Kor in Iran is a synonym.

Further reading. Bianco & Bănărescu 1982 (description of C. orientale); Krupp 1985a (record from Orontes); Elvira 1987 (review); Coad 2010a (biology); Ghanbary et al. 2012 (reproductive biology); Jouladeh-Roudbar et al. 2015a (distribution in Iran); Kaya et al. 2016 (distribution); Güçlü et al. 2018 (morphology); Çiftçi et al. 2020 (phylogeny); Coad 2021a (biology, morphology).