Glyptothorax irroratus, Ng & Kottelat, 2023

Ng, Heok Hee & Kottelat, Maurice, 2023, Glyptothorax irroratus, a new species of rheophilic catfish from the Mekong River drainage (Actinopterygii: Siluriformes: Sisoridae), Journal of Natural History 57 (5 - 8), pp. 358-371 : 359-364

Glyptothorax irroratus sp. nov.

urn:lsid:zoobank.org:act:F891B3B2-A01F-4A56-9994-98C51637D002

( Figure 1 )

Glyptothorax trilineatus (not Blyth) – Taki 1974: 81, fig. 80.

Glyptothorax zanaensis (not Wu, He and Chu) – Kottelat 1998: 105, fig. 166; 2001: 138, fig. 383.

Glyptothorax aff. zanaensis – Ng and Rainboth 2008: 68; Kottelat 2016: 300, 316. Glyptothorax dequinensis [sic] (not Mo) – Rainboth et al. 2012: 70, fig. 831 Glyptothorax sp. cf. zanaensis – Rainboth et al., 2012: 70, fig. 845.

Type material

Holotype. MHNG 2788.003 , 69.6 mm SL; Laos: Saysomboune Province , Nam Ngiep at Keng Chong rapids, about 4.5 km upstream of Ban Sopyouak, 239 masl, 18.743°N 103.423° E; M. Kottelat et al., 1 February 2014.

Paratypes. CMK 14107 (1), 67.1 mm SL; Laos: Phongsali Province, Nam Ou at Keng Pang rapids, about 8 km SSE of Ban Hatxa, 21.675°N 102.249°E; M . Kottelat et al., 14 May 1997. UMMZ 240922 (2), 77.2–82.5 mm SL; Laos: Oudomxai Province, Nam Phak , 32 km NE of Muang Xai, 20.883°N 102.167°E; W .J. Rainboth and D. Singhanouvong, 12 April 1997. UMMZ 241062 (1), 63.4 mm SL; Laos: Luang Prabang Province, Nam Xuang, 4 km downstream of Ban Pak Kung , 20.050°N 102.367°E; W .J. Rainboth and K.P. Bouakhamvongsa, 16 March 1998. UMMZ 240664 (1), 66.0 mm SL; Laos: Luang Prabang Province, Nam Xuang at Ban Pak Xuang, 19.967°N 102.500°E; W .J. Rainboth et al., 5 March 1997. UMMZ 240815 (4), 57.1–82.0 mm SL; Laos: Oudomxai Province, Huay Xeng at confluence with Mekong River , 19.883°N 101.117°E; W .J. Rainboth and D. Singhanouvong, 1 April 1997. UMMZ 241857 (1), 71.3 mm SL; Laos: Luang Prabang Province, Nam Phouan at mouth of Mekong River , 19.850°N 101.600°E; W .J. Rainboth et al., 17 January 1998. UMMZ 241106 (12), 50.3– 62.6 mm SL; Laos: Luang Prabang Province, Nam Khan at Keng Noun , 10 km E of Luang Prabang, 19.833°N 102.767°E; W .J. Rainboth and S. Virawong, 17 February 1997. CMK 15230 (1), 70.6 mm SL; Laos: Xiangkhouang Province, Nam Ngum, rapids downstream of Ban Latbouak, 19.608°N 103.240°E; M . Kottelat et al., 30 April 1999. CMK 22633 (17), 30.3– 72.5 mm SL; Laos: Xiangkhouang Province, Nam Ngum upstream of confluence with Nam Ting , 863 masl, 19.398°N 102.914°E; M . Kottelat et al., 22 February 2012. CMK 24384 (12), 62.2–83.9 mm SL; data as for holotype . CMK 13295 (15), 32.4–50.3 mm SL; Laos: Vientiane Province, Nam Leuk, about 500 m downstream of Tad Leuk waterfall, 18.393°N 103.071°E; M . Kottelat et al., 25 February 1997. CMK 12256 (11), 46.4–73.0 mm SL; Laos: Khammouan Province, Nam Theun, waterfall about 7 km downstream of Nakai dam, 18.028°N 104.982° E; M . Kottelat et al., 20 March 1996. CMK 20017 (27), 31.8–76.2 mm SL; Laos: Khammouan Province, Nam Theun at first rapids below Nakai dam, 17.997°N 104.970°E; M . Kottelat et al., 4 April 2007. CMK 12631 (3), 53.2–62.8 mm SL; Laos: Khammouan Province, Nam Theun at Nakai dam, 17.997°N 104.953°E; M . Kottelat et al., 17 March 1996. ZRC 40309 (2), 65.7–76.3 mm SL; Laos: Khammouan Province, Nam Theun, Huay Kor near Ban Nam Nien , 17.933°N 104.983°E; T . R. Roberts and P. Vongsay, 18 November 1995.

Diagnosis

Glyptothorax irroratus differs from Indochinese congeners in having both large and small tubercles arranged irregularly on the lateral surfaces of the body (vs all tubercles of approximately equal size). It is further distinguished from Indochinese congeners except for G. granulus and G. zanaensis in having a uniformly dark grey to black body with only a very faint pale mid-dorsal stripe (vs dark grey to black body with pale mid-lateral and mid-dorsal stripes in G. coracinus , G. deqinensis , G. forabilis , G. granosus , G. interspinalum , G. lanceatus , G. laosensis , G. longicauda , G. longinema , G. porrectus , G. schmidti , G. trilineatus and G. yuensis , and body with pale or dark bands, patches or spots in other species). The following unique combination of characters further distinguishes G. irroratus from Mekong River congeners: eye diameter 9–12% HL; interorbital distance 25–31% HL; head length 23.6–27.8% SL; head depth 13.1–15.7% SL; anteromedial striae in TAA absent; short, triangular medial pit in TAA extending about one-fifth TAA length; TAA width 10.1– 12.0% SL; 7–14 serrae on posterior margin of pectoral spine; dark nuchal plate; neural spines of vertebrae between dorsal and adipose fins distally expanded; body depth at anus 12.2–16.0% SL; uniformly dark-coloured adipose fin, with pale distal margin; length of adipose-fin base 12.5–17.0% SL; post-adipose distance 13.4–18.9% SL; caudal peduncle depth 6.3–7.6% SL (2.6–3.1 times in its length and 1.8–2.1 times in body depth at anus); and caudal peduncle length 17.8–21.4% SL.

Description

Morphometric data in Table 1 . Head depressed; body subcylindrical. Dorsal profile rising evenly from tip of snout to origin of dorsal fin, then sloping gently ventrally from origin of dorsal fin to end of caudal peduncle. Ventral profile straight to anal-fin base, then sloping gently dorsally from anal-fin base to end of caudal peduncle. Anus and urogenital openings located at vertical through posterior quarter of adpressed pelvic fin. Skin tuberculate, with tubercles of uneven sizes on sides of body and caudal peduncle. Vertebrae between dorsal and adipose fins with distally expanded neural spines. Lateral line complete and mid-lateral.

Head depressed and broad, triangular when viewed laterally. Snout prominent. Anterior and posterior nares large and separated only by base of nasal barbel. Gill opening broad, extending from ventral margin of post-temporal to isthmus. First branchial arch with 3 + 6* (2) rakers. Bony elements of dorsal surface of head covered with thick, tuberculate skin. Eye ovoid, horizontal axis longest; located entirely in dorsal half of head.

Barbels in four pairs. Maxillary barbel long and slender, extending to base of second pectoral-fin ray. Nasal barbel slender, extending nearly to anterior orbital margin. Inner mandibular-barbel extending to midway between its base and that of pectoral spine. Outer mandibular barbel extending nearly to base of pectoral spine.

Mouth inferior, premaxillary tooth band partially (approximately half) exposed when mouth is closed. Oral teeth small and villiform, in irregular rows on all tooth-bearing surfaces. Premaxillary teeth appearing in single broad semilunate band. Dentary teeth in a single crescentic band, consisting of two separate halves tightly bound at midline.

Thoracic adhesive apparatus consisting of keratinised striae in an ovate field ( Figure 2 ) extending from isthmus to posterior limit of pectoral-fin base; anterolateral edges of adhesive apparatus gently convex. Triangular medial pit extending for about one-fifth length of TAA, located posteromedially.

Dorsal fin located above anterior third of body, with I,6 (16) rays; distal fin margin concave; spine short and straight, smooth on anterior and posterior margins. Adipose fin with anterior and distal margins nearly straight. Caudal fin strongly forked, with lobes of nearly equal length in some individuals and upper lobe slightly longer than lower in others and i,7,8,i (16) principal rays. Procurrent rays symmetrical and extending only slightly anterior to fin base. Anal-fin base vertically opposite adipose-fin base. Anal fin with straight anterior and distal margins; with iii,8,i (2), iii,9* (4), iv,7,i (1), iii,10 (4), iv,9 (2), iv,9,i (1), iv,10 (1) or v,9 (1) rays. Pelvic-fin origin at vertical posterior to posterior extremity of dorsal-fin base. Pelvic fin with slightly convex margin and i,5 (16) rays; tip of adpressed fin not reaching anal-fin origin. Pectoral fin with I,9 (1), I,9.i* (7) or I,10 (8) rays; posterior fin margin slightly concave; anterior spine margin smooth, posterior margin with 7–14 (holotype = 12) serrations.

Colouration

In 70% ethanol: dorsal and lateral surfaces of head, and body very dark brown, fading to beige on ventral surfaces. A faint thin, cream mid-dorsal stripe extending from base of last dorsal-fin ray to dorsal procurrent caudal-fin rays; stripe broken up into conjoined series of cream patches (delineating distally expanded neural spines) in some individuals; stripe absent in some individuals. Pectoral and pelvic fins with dark brown on base of fin rays and hyaline posterior margin. Anal fin dark brown, with hyaline posteroventral corner, sometimes with a paler or hyaline median band. Dorsal fin dark brown, with hyaline posterior margin, sometimes with a paler or hyaline median band. Adipose fin dark brown, with hyaline distal margin. Caudal fin with dark brown fin rays, hyaline interradial membranes and tip of lobes cream. Maxillary and nasal barbels dark brown dorsally, beige ventrally. Mandibular barbels beige.

In life: As above, but body uniform dark brown to black, mid-dorsal stripe not or poorly distinct. Edge of fins and tip of caudal-fin lobes hyaline to yellow.

Habitat

Glyptothorax irroratus is apparently the most rheophilic species of the genus in the middle and lower Mekong drainage. It has been collected in rapids, waterfalls and other habitats with strong current and with stone, boulder and rocky bottom ( Figure 3 ). It occasionally occurs in areas with weaker current, but always over a stony substrate.

Distribution

Glyptothorax irroratus is known from the middle Mekong River drainage in China and Laos ( Figure 4 ). The record farthest upriver is a single specimen from Xishuangbanna ( China), in Nam Xing River ( Buyuan watershed , 21°53 ʹ 23″N, 101°19 ʹ 41″E; CMK 23958). In Laos, we have seen material from the Nam Phak, Nam Ou, Nam Xuang, Nam Khan, Nam Ngum, Nam Mang, Nam Ngiep, Nam Kading and Xe Bangfai watersheds. It is expected in the Mekong drainage in Thailand and the headwaters of Nam Ou in Dien Bien province in Vietnam. Its presence farther downstream in the Mekong drainage cannot be excluded. Glyptothorax irroratus possibly also occurs in the Chao Phraya drainage in Thailand, with a single specimen collected from Chiangmai showing the tubercles, TAA, expanded neural spines and colour pattern diagnostic for G. irroratus (CMK 4099, 19°30 ʹ 29″N, 98° 57 ʹ 31″E).

Etymology

The Latin adjective irroratus (- us, -a, -um) means covered with dew; in zoology used to mean besprinkled with drops or particles. This is used in allusion to the irregular tuberculation on the sides of the body and caudal peduncle.

Figures

Figure 1. Glyptothorax irroratus, holotype, MHNG 2788.003, 69.6 mm SL; Laos: Nam Ngiep. Dorsal, lateral and ventral views. Note unusual tuberculation on sides of body and caudal peduncle.

Figure 2. Thoracic adhesive apparatus of Glyptothorax irroratus, holotype, MHNG 2788.003, 69.6 mm SL.

Figure 3. Type locality of Glyptothorax irroratus (Nam Ngiep at Keng Chong rapids, Laos).

Figure 4. Map showing collection localities of Glyptothorax irroratus (see the Supplementary material for additional localities not mentioned in the main text).