Altigena sinkleri (Fowler 1934)

Figures 1 and 2

Labeo sinkleri Fowler 1934:130, figs. 93–94.

Type locality: Thailand, Metang River (= Mae Tang), 35 miles north of Chieng Mai. Holotype: ANSP 58423

Bangana sinkleri.— Kottelat 1998

Diagnosis. A member of Altigena based on characters listed by Kottelat (2017). Altigena sinkleri can be distinguished from all species in the genus by the following combination of characters: 28–31 + 2–4 lateral-line scales and pored scales on caudal fin (31–34 total pored lateral scales); 8–12 (mode 10) predorsal scales; 3½ scale rows between the dorsal-fin insertion and lateral line; 12–16 (mode 14) circumpeduncular scales; 9½–10½ (mode 9½) branched dorsal-fin rays; tubercles on tip of snout (when present) bicuspid; fins of juveniles with orange coloration.

Description. Morphometrics and meristics in Table 1. Mouth inferior, strongly arched. Rostral cap thick, pendulous; crenulated medially, smooth laterally, separated from upper lip by deep groove, covering all but edge of upper lip. Upper lip entirely enclosing upper jaw, edge smooth, continuous with labial fold at corners of mouth. Anterior edge of labial fold papillose, separate from lower jaw by deep grove. Plical groove present. Pair of gular grooves present, connected with plical groove (Fig. 1). Maxillary barbels, if present, small. Three rows of tubercles on tip of snout, sublachrymal grooves on sides of rostral cap partially divide anteriormost row from posterior rows; tubercles on tip of snout, when present, bicuspid, remaining unicuspid. Shallow ethmoidal furrow present, separating 3 rows of tubercles on snout from row of small tubercles between nares.

Dorsal profile slightly arched, deepest at dorsal-fin insertion. Ventral profile slightly concave. Head short, longer than wide; snout conical, rounded when viewed from dorsal side; eyes dorsolateral. Dorsal-fin origin anterior of pelvic-fin origin. Pectoral fins positioned ventrally, reaching approximately ⅔ from origin to pelvic-fin origin when adpressed. Pelvic fins reaching approximately ¾ to anal fin when adpressed. Anal fin just reaching insertion of caudal-fin when adpressed. Dorsal and anal fins concave; pectoral and pelvic fins triangular. Caudal fin forked, upper and lower lobes of equal length. Axillary pelvic lobes well-developed.

Dorsal fin with 3 simple and 9½–10½ branched rays; anal fin with 3 simple and 5½ branched rays; pelvic fin with 1 simple and 7–8 branched rays; pectoral fin with 1 simple and 14–16 branched rays; caudal fin with 10+9 principal rays, 9+8 branched. Body entirely scaled except for predorsal midline; scales on chest smaller and more embedded than on remainder of body. Lateral-line scales 28–31 + 2–4 pored scales on caudal fin; total pored lateral scales 31–34; predorsal scales 8–12; scale rows between dorsal-fin insertion and lateral line 3½; scale rows between anal-fin insertion and lateral line 3½–4½; scale rows between pelvic-fin origin and lateral line 2½–3½; circumpeduncular scales 12–16.

In preservative (Fig. 2), body light brown dorsally, cream ventrally. Faint darker brown bar present at caudal-fin base. Fins clear except for tiny melanophores on interradial membranes of dorsal and caudal fins.

Distribution. Altigena sinkleri was described from the Mae Tang River, which empties into the Ping River in the Chao Phraya basin in northern Thailand. Suvarnaraksha (2016) reported this species from the Mae Chaem River, another tributary of the Ping River. This species has also been collected from the Hueang River (Mekong River basin) in Loei Province of eastern Thailand. One lot of specimens examined (NIFI 03289) is listed from the Mun River in the Chiang Khan District of Loei Province; however, the Mun River does not flow through this province. It is thus unclear where these specimens were collected, although the Chiang Khan District is the location of the mouth of the Loei River, approximately 11.5 km downstream of where the Hueang River enters the Mekong River.

Comparisons. Ciccotto et al. (2021) distinguished A. sinkleri from all species of Altigena except A. malihkaia Zheng, Win & Chen based on the presence of 14 circumpeduncular scales in the two type specimens examined (compared to 16 or more circumpeduncular scales in all other species). However, additional non-type specimens from the Mae Tang River were observed to have 14–16 circumpeduncular scales, necessitating this revised diagnosis. Altigena sinkleri can be distinguished from A. malihkaia, A. tonkinensis (Pellegrin & Chevey), A. wui (Zheng & Chen), A. yunnanensis (Wu & Lin), and A. zhui (Zheng & Chen) in possessing fewer total pored lateral scales (31–34 vs. 41 or more). Altigena sinkleri can be distinguished from A. laticeps and A. discognathoides (Nichols & Pope) in possessing fewer predorsal scales (8–12 vs. 14–16) and further distinguished from A. laticeps in possessing fewer circumpeduncular scales (16 or less vs. 20).

Altigena elegans and A. lippa both possess higher numbers of scale rows between the dorsal-fin insertion and lateral line compared to A. sinkleri (4–4½ in A. elegans and 5½ in A. lippa vs. 3½ in A. sinkleri). Altigena sinkleri is further distinguished from A. lippa in possessing fewer lateral-line scales (28–31 vs. 32–36). Additionally, A. sinkleri possesses modally fewer branched dorsal-fin rays (9½ [8 specimens], 10½ [2] vs. 10½ [2] in A. elegans and 9½ [3], 10½ [12] in A. lippa), modally fewer circumpeduncular scales (12 [2], 13 [1], 14 [4], 15 [2], 16[1] vs. 16 in A. elegans and A. lippa), and bicuspid tubercles (vs. unicuspid in A. elegans and A. lippa) on the tip of the snout, when present. In the original description of A. elegans, Kottelat (1998) reported all type specimens (n=8) to have 10½ branched dorsal-fin rays and a presumed number of 16 circumpeduncular scales (therein reported as 3½, 1, 3½ on one side) as well. All specimens of A. sinkleri from the Mekong River basin examined here possess 9½ branched dorsal-fin rays and 12–14 circumpeduncular scales; only specimens from the type locality in the Chao Phraya (= Mae Tang) occasionally possess 10½ branched-dorsal rays and 15–16 circumpeduncular scales. The fins of juvenile A. elegans are olive-green compared to the orange fins of A. sinkleri and A. lippa (Kottelat 1998, Suvarnaraksha 2006, Rainboth et al. 2012).

Comments. Specimens of A. sinkleri housed at NIFI date from 1989–1994. Searches in other institutional collections have not yielded more recent records of A. sinkleri, although the specimens shown in Suvarnaraksha (2016) were possibly collected more recently. The limited number of vouchered records of A. sinkleri is similar to what is observed in other species of Altigena, which may reflect preferences for difficult to sample habitats, temporal variation in habitat use, and/or declining populations throughout the region (Ciccotto et al. 2021).

Altigena sinkleri.

ANSP 58423, 1 (holotype), 74.2 mm SL, Thailand, Metang River, tributary of Me Nam Ping, 35 mi. N. of Chieng Mai; ANSP 58423, 1 (paratype), 68.8 mm SL, same data as ANSP 58423; NIFI 02946, 4, 83.1–101.5 mm SL, Thailand, Maetang, Chiangmai; NIFI 03004, 4, 154.2– 170.7 mm SL, Thailand, Hueang River, Dai Sai, Loei; NIFI 03289, 3, 136.3– 162.9 mm SL, Thailand, Mun River, Chiang Khan, Loei.