Oreoglanis omkoiense, Suvarnaraksha, 2020

Suvarnaraksha, Apinun, 2020, Oreoglanis omkoiense: a new torrent catfish from northern Thailand (Pisces: Siluriformes, Sisoridae), Raffles Bulletin of Zoology 68, pp. 779-790 : 780-786

Oreoglanis omkoiense , new species

( Fig. 1 )

Diagnosis. Oreoglanis omkoiense , new species, belongs to the O. siamensis species group, as it possesses a distinct median notch on the posterior margin of the lower lip. This species differs from its congeners in having the following combination of characters: maxillary barbel with pointed tip, long nasal barbel 25.0–32.9%SL, long pre-dorsal 33.2–39.2%SL, pre-ventral length 36.1–39.2%SL, height of dorsal fin 15.4–20.3%SL, length of adipose fin 32.3– 39.6%SL, post-adipose length 5.7–8.8%SL, caudal peduncle depth 2.1–3.3 times its length, head width 18.7–22.9%SL and 90.2–96.8%HL, eye diameter 9.2–13.1%HL, inner mandibular barbel 21.8–30.5%HL, and an emarginate caudal fin with upper and lower first principal rays of approximately equal length.

Description. Oreoglanis omkoiense has four pairs of barbels: nasal barbels long, reaching anterior orbital margin; maxillary barbels flattened with membranous flap of skin on dorsoposterior edge and rounded tip, with numerous plicae on ventral surface and crenulated ventroposterior edge; inner mandibular barbels originating close to midline, immediately under lower lip and extending to imaginary line through bases of the first pectoral-fin elements; and outer mandibular barbels originating posterolateral to inner mandibular barbels, extending to base of first pectoral-fin element. Morphometric data of the holotype and 10 paratypes are provided in Table 1.

Head moderately broad and extremely depressed; dorsal profile slightly convex and ventral profile almost straight. Eye ovoid, horizontal axis longest, subcutaneous; located dorsally on head. Gill openings extremely narrow, extending from middle of pectoral fin base to level just medial to base of last pectoral-fin ray. Mouth inferior, with broad, thin, and papillate lips. Lower lip with median notch, posterior margin with lobulated projections. Post-labial groove on lower jaw uninterrupted. Two types of teeth present on jaw; anterior teeth short and spatulate, with curved inner face, and posterior teeth pointed ( Fig. 2 ).

Anterior half of body extremely depressed, and compressed towards caudal peduncle. Head and snout rounded. Dorsal profile rising very gently from tip of snout to origin of dorsal fin, then almost horizontal to end of adipose-fin base, sloping gently ventrally thereafter to end of caudal peduncle. Ventral profile horizontal to anus and thereafter sloping dorsally to end of caudal peduncle. Skin smooth. Lateral line complete and mid-lateral in position. Total number of vertebrae 33–36, consisting of 14 + 19 = 33 (n = 2), 15 + 18 = 33 (n = 1), 15 + 19 = 34 (n = 2), 15 + 20 = 35 (n = 1), 15 + 21 = 36 (n = 1), 16 + 17 = 33 (n = 1), and 16 + 18 = 34 (n = 1) ( Fig. 3 ).

Dorsal fin with first element not ossified, i,6 (n = 11) with fin margin convex. Pectoral fin greatly enlarged, with first element thickened but not ossified, i,15,i (n = 3), i,17,i (n = 5), or i,18,i (n = 3). Ventral surface of thickened first pectoral-fin element with numerous striae. Pectoral-fin margin strongly convex. Pelvic-fin origin at mid-point of body. Pelvic fin enlarged, i,5 (n = 11) with convex margin. Ventral surface of first pelvic-fin element with numerous striae. Anus and urogenital openings located at vertical line through posterior quarter of adpressed pelvic fin ( Fig. 4 ). Anal fin with short base, i,5 (n = 11). Caudal peduncle short. Caudal fin emarginate, i,6,6,i (n = 11).

Sexual characters. Male with small conical-shaped genital papilla located immediately posterior to anus, and its tip at posterior end of pelvic fin ( Fig. 4A, C ). Female with tubelike genital papilla located immediately posterior to anus ( Fig. 4B, D ).

Colouration. Live specimens: dark brown on dorsal and lateral surfaces of head and body, light yellow on ventral region. Dorsal surfaces of head and body with series of small, light yellow patches: two ovoid patches twice the eye diameter on occipital region. Dorsal-fin base brown, bright yellow-brown on lower part, dorsal surfaces of pectoral and pelvic fins brown, anal fin and ventral surfaces of pectoral and pelvic fins light yellow, and all fins tipped with pale or white. Adipose fin light yellow. Caudal fin brown with two round bright yellow-orange patches approximately one- third of caudal fin lobe, and caudal fin tip with light orange. Pectoral-fin base occasionally with round yellow patch on both inner and outer anterior sides. Dorsal surface of barbels brown, ventral surface light yellow ( Fig. 1 ).

Colour in 70% ethanol: brown on dorsal and lateral surfaces of the head and body, dark yellow on ventral region. A paler, dark light brown ovoid patch at the base of the first dorsal-fin element present. Dorsal and caudal fins brown; dorsal surfaces of pectoral and pelvic fins brown, with light yellow ventral surfaces. Anal fin light brown. Dorsal surface of barbels brown, ventral surface light yellow. Caudal fin base with a vertical darker band that extends along outermost lower principal caudal rays.

Ecology, food, and reproductive biology. Oreoglanis omkoiense , new species, lives in high land streams, on the bottom of cool, clear, fast-flowing streams with pools and 60% forest canopy. Oreoglanis omkoiense was collected from 1,138 m above sea level in high altitude gradient streams in Huai Jino, a tributary of the Ping River basin ( Fig. 5 ). Huai Jino was approximately 1–2 m wide and 0.2–0.5 m deep at the time of sampling (start of the hot dry season); water volume might be much higher during the rainy season. This species was observed in shaded areas with pebbles, stones, and gravel substrates ( Fig. 6 ). The upper stream bank was covered by large native trees with good canopy cover. The water was clear and fast running, and the temperature was 18.5°C (air temperature 25.5°C). Other species of fishes collected with O. omkoiense were Devario spp. , Schistura spp. , and Channa gachua . Gut dissections indicated that O. omkoiense feeds mainly on aquatic insect larvae and diatoms.

Etymology. Named after Omkoi, the district of the locality where the new species was discovered.

Distribution. Found in the Metuen River basin, a tributary of the Ping River drainage (one of four main tributaries of the Chao Phraya River), in Chiang Mai, Thailand.

Suvarnaraksha: Highland stream freshwater batfish from Maeping River Basin

Figures

Fig. 1. Oreoglanis omkoiense, new species, Huai Jino, Baan Huai Jino, Omkoi Subdistrict, Omkoi District, Chiangmai Province. Holotype, MARNM 6447, 91.86 mm SL. (A = lateral view, B = dorsal view and C = ventral view)

Fig. 2. Comparison of lower lip with median notch and posterior margin entire in Siamensis species group: A, Oreoglanis omkoiense, new species, paratypes, MARNM 4334, 78.54 mm SL; and B, O. siamensis MARNM 6338, 87.18 mm SL, and Delacouri species group: C, O. laciniosus MARNM 6345, 73.41 mm SL; and D, O. tenuicauda MARNM 6339, 61.90 mm SL.

Fig. 3. Tooth on upper jaw (A) and lower jaw (B) with outer spatula teeth and inner pointed teeth in Oreoglanis omkoiense, new species (uncatalogued).

Fig. 4. Comparison of skeleton system of some Oreoglanis spp. in Thailand. A, O.siamensis MARNM 6338; B, O. laciniosus MARNM 6345; C, O. sudarai MARNM 6332; D, O. nakasathiani MARNM 6340; E, O. suraswadii MARNM 6339; F, O. omkoiense, new species, MARNM 6334.

Fig. 5. Ventral view of anus and external genital papilla of Oreoglanis omkoiense, new species. A, MARNM 7141, paratype, female, 90.26 mm SL; B, MARNM 6333, holotype, male, 91.86 mm SL.

Fig. 6. Map of type locality of Oreoglanis omkoiense, new species, holotype, MARNM 6333, 91.86 mm SL. Thailand: Chiangmai: Omkoi District.