Glyptothorax cous ( Linnaeus, 1766 )

Glyptothorax cous ( Linnaeus, 1766) View in CoL

( Fig. 10–17 View FIGURE 10 View FIGURE 11 View FIGURE 12 View FIGURE 13 View FIGURE 14 View FIGURE 15 View FIGURE 16 View FIGURE 17 )

Silurus cous Linnaeus, 1766:504

Material examined. BMNH 1955.6.25.2, 200 mm SL; Syria: Coic (Qweiq) River (photographs only).—FFR 3909, 1, 62 mm SL; Turkey: Siirt prov.: stream Gökçesu   GoogleMaps 15 km southwest of Siirt, 37.8219 41.8280.—FFR 3911, 1, 55 mm SL; FFR 3919, 1, 210 mm SL; Turkey: Siirt prov.: Botan River   GoogleMaps 9 km southwest of Siirt, 37.8525 41.8872. —FSJF 3952, 1, 52 mm SL; Iraq: Great Zab about 2 km upriver of confluence with Rawanduz   GoogleMaps , 36.7484 44.2997.—FSJF 3530, 1, 155 mm SL; Iraq: Shatt al Arab   GoogleMaps at Basra, 30.5395 47.8312.—FSJF 3820, 2, 165–185 mm SL; FSJF 3975, 3, 145–183 mm SL; Iraq: Aw-e Shiler River at Khewata   GoogleMaps , 35.7511 45.4792.— SMF 517 About SMF , 1, 171 mm SL; Syria: probable from Qweiq at Aleppo.— SMF 23677 About SMF , 2 About SMF , 62–118 mm SL; Syria: Nahr Al-Khabur about 16 km south-east of al-Hasaka, 36.43 40.87.— SMF 28696 About SMF , 29 About SMF , 129–222 mm SL; Syria: Euphrates at Raqqa, 35.93 38.99.— SMF 28704 About SMF , 1 About SMF , 76 mm SL; Syria: Euphrates below Baath Lake , 35.92 38.87.— SMF 28728 About SMF , 2 About SMF , 144–160 mm SL; Syria: Euphrates between Raqqa and Halebye-Zalebye , 35.93 38.93.— NMW 46475 , 1, 123 mm SL; NMW 46476 , 2 , 92–132 mm SL; NMW 46477 , 1, 184 mm SL; NMW 55836 , 1, 185 mm SL; NMW 46478 , 1, 197 mm SL; NMW 46479 , 1, 157 mm SL; Syria: Qweiq at Aleppo (photographs only).— NMW 94378 , 3 , 98–185 mm SL; Armenia [most likely from Turkey: Euphrates] (photographs only).—ZMH 4430, 2, 130–131 mm SL; Turkey: Erzincan prov.: Euphrates at Kemalye   GoogleMaps , 39.2625 38.5019.

Material used in molecular genetic analysis. FSJF-DNA 2648; Iraq: Great Zab about 2 km upriver of confluence with Rawanduz River, 36.7484 44.2997 (GenBank accession number: MW770727 View Materials ) GoogleMaps .— FSJF-DNA 2626; Iraq: Aw-e Shiler River at Khewata, 35.7511 45.4792 (GenBank accession numbers: MW770715, MW770716, MW770719 ) GoogleMaps .— FSJF-DNA 3340–3348; Iraq: Qal’ah Chwalan River at Bardbard, 35.9150 45.36772 (GenBank accession numbers: MW724504 View Materials – MW724511 View Materials ) GoogleMaps .

Diagnosis. Glyptothorax cous is distinguished from its congeners in the Euphrates and Tigris drainages by a combination of characters, none of them unique. It is distinguished from G. armeniacus by having many large, bony, striated and elongated tubercles on the head, back and flank (absent in some individuals) (vs. with very small tubercles and roundish warts), the thoracic adhesive apparatus 0.8–1.1 times longer than wide (vs. 1.0–1.5), poorly delineated at its posterior margin (well delineated), only partly situated on a shallow, horse-shoe shaped swelling (vs. completely situated on the swelling); swelling absent in many adult individuals (vs. always present), striae of the thoracic adhesive apparatus reaching far beyond the swelling, usually onto the pectoral-fin base (vs. restricted to swelling), usually many or few large, bold, dark-brown blotches on the flank in preserved individuals (vs. flank usually plain brown or with small and indistinct brown spots or small blotches). See below for characters to distinguish G. cous from other Glyptothorax in the Middle East.

Other characters useful for identification are: Caudal-peduncle depth 1.6–2.3 times in its length, adipose-fin short, its length 0.6–1.2 times larger than distance between base of last dorsal-fin ray and adipose-fin origin; head blunt, spade-shaped, 28–33% SL; thoracic adhesive apparatus usually extending from isthmus to base of last pectoral-fin ray or to posterior limit of pectoral-fin base; anteromedial striae numerous and well developed; medial pit without striae; flank with large, dark-brown blotches and/or small dark-brown spots. Size up to 347 mm SL.

Distribution Widespread in the Euphrates and Tigris drainages including the Karkheh subdrainage in Iran (recorded from Seimare River). Was formerly known from the Qweiq, but has vanished from that river. Not recorded from the Karun. Occurs in syntopy with G. steindachneri in Syria and with G. kurdistanicus in the Lesser Zab in Iraq.

Remarks. Russell (1756) in his “Natural History of Aleppo ” described one individual collected from the Coic (Qweiq) River. Gronow (1763) based his account of „ Mystus cirris octo , capite brevioribus, pinna dorsi fecunda ovata ” on the fish described by Alexander Russell and Linnaeus (1766) based his description of Silurus cous on these two accounts. The individual BMNH 1955.6.25.2 ( Fig. 10 View FIGURE 10 , Fig. 13 View FIGURE 13 ) is the one collected by Russell and is therefore the surviving type (James MacLaine, pers. comm. 2020). Russel lived in Aleppo between 1740 and 1756 and BMNH 1955.6.25.2 is not the only fish housed at BMNH from his collection (James MacLaine, pers. comm. 2020). Heok Hee Ng (pers. comm. 2021) raised some doubts on the type status of this specimen as it is remarkably well-preserved and seems to be formaline preserved, what was not the rule in Russell’s times. But we see no way to test, if BMNH 1955.6.25.2 is or is not the type of G. cous . Russel (1756) provided a quality drawing of a lateral ( Fig. 15 View FIGURE 15 ) and dorsal view of the fish taken from the Coic (Qweiq) River in Aleppo, which must be considered as a syntype. Even from these drawings only, G. cous can be distinguished from the two species known from the adjacent Euphrates (short adipose fin vs. long in G. steindachneri ; pale yellowish background colour with many bold black or dark-brown spots vs. brown background colour with few spots in G. armeniacus ). Furthermore, all materials examined from SMF and NMW from the Qweiq (see above) are identified as G. cous . Therefore, we have no doubts that the syntypes from which the drawing by Russell (1756) was made from as well as BMNH 1955.6.25.2 are conspecific with the species identified here as G. cous , irrespective if BMNH 1955.6.25.2 is the fish on the drawing or not.

Linnaeus (1766) description is not informative but Russel (1756) provided a good drawing of a lateral ( Fig. 15 View FIGURE 15 ) and dorsal view of the fish taken from the Coic (Qweiq) River in Aleppo. The name Arius cous , which appeared in Heckel (1843) and in Hyrtl (1859), is based on Silurus cous (Linnaeus) and is not an available name even though it has been treated as such ( Ferraris, 2007).

Glyptothorax cous is the very first Sisorid catfish described by European scientists ( Linnaeus, 1766), but early authors working on the fishes of the Euphrates and Tigris seem not to have been aware of G. cous as a valid species. The placement of Silurus cous in Arius might have been one of the reasons, why this species had so long been ignored in the literature about the fishes of the Euphrates and Tigris. Neither Pietschmann (1913) when describing G. steindachneri, Berg (1918) in the description of G. armeniacus , nor Berg (1931) in the description of G. kurdistanicus did mention G. cous and therefore, the differences to their new species and G. cous remained unclear. Only Coad (1981), when describing G. silviae , included G. cous in his identification key. He was apparently not aware of the existence of the type and identified BMNH 1968 12.13.471–476 as G. cous . We re-examined BMNH 1968 12.13.471–476 and identify them as G. steindachneri .

The identification key given by Coad (1981) for Glyptothorax in the Middle East is quite confusing, as Coad (1981) identified G. cous having a long pectoral fin, reaching to the pelvic-fin origin. But the type of G. cous ( Fig. 10 View FIGURE 10 ) has a short pectoral fin, not reaching to the pelvic-fin origin, a character state also clearly seen in the drawing by Russell (1756) ( Fig. 15 View FIGURE 15 ) reproduced by Coad (2010) without further discussion. Surprisingly, there is materials at NMW identified by Coad as G. cous despite having a short pectoral fin, and we confirm these identifications.

Glyptothorax cous is widespread in the Euphrates and Tigris and has been found in all countries of the catchment basin. But as a note of caution, we have to mention that all our molecular data of G. cous come from fish caught in the Tigris drainage, while G. cous was described from the Qweiq, a former tributary of the Euphrates and most of the fish examined for the morphological characters by us come from the Euphrates. This bias is based on the very limited availability of materials from the Euphrates. The Qweiq has almost completely dried out and no water remains in the entire Syrian part of the catchment. In Turkey, there are two very small streams, the Sünnep, and the Balıksuyu, which belong to the Qweik catchment. JF and CK visited the Sünnep several times and Dağlı & Erdemli (2009) published about the fishes of the Balıksuyu without record of Glyptothorax . Furthermore, Davut Turan (pers. comm.) informed us that he never found Glyptothorax in these streams. Therefore, we expect that G. cous has vanished from the Qweiq.

Most individuals, including juveniles, of G. cous have large, elongated and striated bony tubercles on the head and skin of the body ( Fig. 14 View FIGURE 14 ). But there is a surprising variability in this character and several individuals lack tubercles completely and these are also not visible in the type specimen. The presence or absence of tubercles is not to be dependent on the gender of the fish. As all freshly collected and carefully preserved fish have well developed tubercles, is seems possible that these are scraped off in poorly preserved individuals. But skin moulting cannot be fully excluded.

Preserved individuals of G. cous ( Fig. 11 View FIGURE 11 ) have a grey or yellowish background colour with large or small dark-brown blotches or spots. In life ( Fig. 16–17 View FIGURE 16 View FIGURE 17 ), there are two colour types, similar to what is observed in G. daemon (see below). In the Lesser Zab, a tributary of the Tigris, we found several individuals ( Fig. 17 View FIGURE 17 ) with a dark-brown or dark-grey, almost black background colour, a pattern of dark-brown blotches or spots and many small, whitish spots. These brown individuals occur in sympatry with yellow individuals and both are indistinguishable in our molecular analysis. All brown individuals turned pale-grey in formaline and are no longer distinguished from the yellow individuals, also the yellow colour faded after preservation. Only two individuals (FSJF 3820), which were preserved in formaline after having been frozen, kept their dark-grey colouration. Potentially such different colour forms occur also in other Glyptothorax as we have just not seen enough live individuals of the other species.