Amblyceps waikhomi sp. nov.

urn:lsid:zoobank.org:act: 8F9219B2-619E-4321-8C2E-F31926DAD0FF

Type specimens

Holotype. ZSI/APRC/P-1125, 42.9 mm SL; India, Arunachal Pradesh, Namsai District, Nongkon stream at Nongkon village draining into Noa Dehing River (Brahmaputra basin), 27° 36’05”N, 95°50’51”E; Akash Kachari, 5 October 2013.

Paratypes. Locality and collector as for holotype, RGUMF 269, 40.2 mm SL, 1 cleared and stained (c&s), 20 June 2014; RGUMF 270, 37.4 mm SL, 1 c&s, 12 October 2014; RGUMF 271, 30.4–44.7 mm SL, 2, 6 December 2014.

Diagnosis

Amblyceps waikhomi sp. nov. (Fig 1, S1 Fig) differs from all congeners in having a deeper body (depth at anus 17.0–20.3% SL vs. 7.6–16.9) and fewer (except A. mangois and A. serratum) total vertebrae (34–35 vs. 37–48) (S1 Table). It differs from A. mangois in lacking (vs. having) strongly-developed projections on the proximal lepidotrichia of the median caudal-fin rays and in having a longer, wider, and deeper head (S2 Table) (length: 22.1–24.3% SL vs. 18.8– 21.3, width: 20.0–21.9% SL vs. 17.1–18.3, depth: 13.9–18.0% SL vs. 11.6–13.2); and from A. serratum in having a posteriorly smooth (vs. with 4–5 serrations) pectoral spine, and unequal jaw length (lower jaw longer and weakly-projecting anteriorly vs. equal upper and lower jaws). It additionally differs from A. murraystuarti, A. torrentis, A. apangi, A. laticeps, and A. cerinum in having a deeply forked (vs. emarginate or truncate) caudal fin.

Description

Morphometric data are shown in Table 1. Body short, stout, laterally compressed. Dorsal profile rising evenly from tip of snout to dorsal-fin origin, then straight upto middle of adipose-fin base, thereafter gently sloping ventrad to the end of caudal peduncle. Ventral profile convex up to anal opening, then gently sloping dorsally up to end of anal-fin base, thereafter gently sloping ventrad towards caudal-fin base. Anus and urogenital openings located slightly anterior to anal-fin origin.

Head depressed. Snout rounded. Mouth terminal with unequal jaws, lower slightly longer; lips papillate, with double fold of thickened skin. Premaxillary tooth band semicircular, bearing short, conical, posteriorly directed teeth. Mandibular teeth short, conical, arranged in narrow crescentic band. Eye small, rounded, and subcutaneous. Anterior nostril short, tubular, situated immediately anterior to base of nasal barbel. Nasal barbel extending beyond upper margin of upper gill opening, not reaching posterior margin of opercle. Maxillary and outer mandibular barbels reaching to base of last pectoral-fin ray. Inner mandibular barbel extending to base of pectoral-fin. Skin on head and body tuberculate. Lateral line incomplete, curved downward, and terminating at a point slightly anterior to vertical through dorsal-fin origin. First branchial arch with 2+7 (n = 5) gill rakers. Gill membranes narrowly joined at isthmus, with 10 (n = 2) branchiostegal rays.

Dorsal fin with a spinelet, a spine, and 6 (n = 5) branched rays; its origin closer to snout tip than to adipose-fin origin; posterior margin of fin convex; fin base fleshy and swollen. Dorsal-fin spine smooth, short and straight, distal tip sharply pointed, its length reaching one-third of fin height. Adipose fin short, low, commencing from vertical midway between anus and anal-fin origin, posterior margin well separated from caudal fin. Pectoral fin with a smooth spine and 6 (n = 5) branched rays; origin anterior to vertical through posterior margin of operculum posterior margin convex. Pectoral-fin spine longer than dorsal-fin spine, straight, anterior and posterior margins smooth. Skin covering pectoral-fin base and skin covering spine swollen. Pelvic fin with i–ii,4–5 rays, tip of adpressed fin reaching beyond urogenital opening but not anal-fin origin. Anal fin with iii,10 rays. Caudal fin deeply forked with i,7,8,i (n = 5) principal rays, simple-principal and segmented procurrent rays of upper and lower lobe bears pinnate like rays anteriorly, upper lobe longer than lower (S2 Fig).

Coloration. In 70% ethanol: Dorsal and lateral surfaces of head and body brownish, ventrally creamy.

Distribution. Presently known only from its type locality, Nongkon stream draining to Noa Dehing River (Brahmaputra basin), Namsai District, Arunachal Pradesh (Fig 2).

Habitat. The new species was collected from a slow moving stream (water current 0.16 m / s) with a bottom substrate dominated by sand, occasionally associated with mud (Fig 3). The species was often encountered under submerged logs and bamboo. Water hyacinth was the dominant macrophyte of the stream. Chemical parameters of the stream were DO 6.75 mg /l, DCO 2 1.53 mg /l, alkalinity 66.06 mg /l, and hardness 71.8 ± 3.05 mg /l; while the physical parameters were pH 6.78, air temperature 23.8 ±0.87°C, water temperature 23.5 ±0.96°C, transparency 79.5 ± 1.93 cm,and conductivity 173.33 μS.

doi:10.1371/journal.pone.0147283.t001

Etymology. The new species is named after Waikhom Vishwanath, honouring his outstanding contribution to freshwater ichthyology in the Indian subcontinent.

Discussion

Amblyceps species have unossified pinnate-like rays (4–5 pinnate rays per lepidotrichium) on the anterior margins of the procurrent caudal-fin rays [2]. In the present study, we examined cleared and stained specimens of A. mangois, A. arunachalensis, A. apangi, and A. waikhomi and found the pinnate like rays (except A. apangi) only on the distal half of the anterior margin of the segmented procurrent rays and unbranched principal rays. Ng and Kottelat [9] further reported the presence of pinnate like rays along the median caudal-fin rays of Amblyceps of the Indian subcontinent. This finding was confirmed by our observations on A. mangois (Fig 4a; S 3 Fig) and A. arunachalensis (Fig 4b), which exhibited strongly-developed ossified projections on the proximal lepidotrichia of the median caudal-fin rays. However, this feature was absent in A. waikhomi (Fig 4c) and A. apangi. In A. arunachalensis these ossified projections were

hypural in A. waikhomi, not shown in figure). [Ph: parhypural, H: hypural plate, Dr: depression, E: epural, C: centrum Uprr: upper procurrent ray, Uspr: upper simple principal ray, Ubpr: upper branched principal ray, Sdp: strongly developed-projections, Lbpr: lower branched principal ray, Lspr: lower simple principal ray]

doi:10.1371/journal.pone.0147283.g004

observed between the two lowermost branched principal rays of the upper lobe, between the two uppermost branched principal rays of the lower lobe, and also between the lowermost and the uppermost rays of the upper and lower lobe of the caudal fin respectively. In the case of A. mangois, these projections were located only between the two lowermost branched rays of the upper lobe of caudal fin.

With the description of Amblyceps waikhomi, seven species of Amblyceps are now known from the Ganga-Brahmaputra River system viz. A. waikhomi, A. mangois, A. arunachalensis, A. tenuispinis, A. apangi, A. laticeps, and A. cerinum. Amblyceps species can be divided into two groups: one having a deeply forked caudal fin, and the other with an emarginate or truncate caudal fin. In addition to the characters mentioned in the diagnosis (specifically for the congeners in the first group, to which A. waikhomi belongs), A. waikhomi further differs from A. tenuispinis in having a shorter snout (23.4–27.2% HL vs. 33.6–43.3) and dorsal to adipose distance (17.0–21.3% SL vs. 23.9–34.0), a longer pectoral fin (16.8–19.0% SL vs. 15.1–16.6), and a deeper caudal peduncle (13.0–16.4% SL vs. 9.6–12.9); from A. arunachalensis in having a longer predorsal (25.7–30.6% SL vs. 22.5–23.2), prepelvic (48.3–50.3% SL vs. 45.1–45.9), prepectoral (19.2–23.0% SL vs. 18.2–19.8), and adipose-fin base (20.3–23.7% SL vs. 18.1–19.8) lengths and fewer pleural ribs (7 vs. 12); and from A. macropterus in having fewer vertebrae (34–35 vs. 37), a shorter adipose-fin base (20.3–23.7% SL vs. 28.3), and in lacking (vs. having) the strongly-developed projections on the proximal lepidotrichia of the median caudal-fin rays.

Amblyceps waikhomi can be further distinguished from A. carinatum by its shorter adipose-fin base length (20.3–23.7% SL vs. 37.5–44.6) and longer dorsal to adipose distance (17.0– 21.3% SL vs. 7.8–10.7); from A. tuberculatum by its shorter caudal peduncle length (15.5– 18.6% SL vs. 21.2–22.4), shorter dorsal to adipose distance (17.0–21.3% SL vs. 27.8–28.0), and incomplete (vs. complete) lateral line; from A. kurzii by its longer adipose-fin base (20.3–23.7% SL vs. 15.1–18.3), shorter dorsal to adipose distance (17.0–21.3% SL vs. 30.1–30.6), and deeper caudal peduncle (13.0–16.4% SL vs. 9.8–10.7).

Amblyceps waikhomi can be further distinguished from A. platycephalus by its fewer principal caudal-fin rays (17 vs. 20); from A. caecutiens in having a larger eye (6.7–7.5% HL vs. 2.0– 3.4) and shorter adipose-fin base (20.3–23.7% SL vs. 25.6–33.5); from A. protentum in having a longer prepelvic (48.3–50.3% SL vs. 42.8–47.8), prepectoral (19.2–23.0% SL vs. 15.9–18.3), and pectoral-fin (16.8–19.0% SL vs. 11.2–14.4) lengths, shorter and deeper caudal peduncle (length:15.5–18.6% SL vs. 20.0–25.6; depth: 13.0–16.4% SL vs. 8.0–10.3), shorter snout (23.4– 27.2% HL vs. 30.1–34.6), and shorter dorsal to adipose distance (17.0–21.3% SL vs. 26.3–32.2); and from A. variegatum by its uniformly brownish (vs. mottled) body coloration.

Comparative material

Amblyceps mangois: ZSI-NRS / F2556, 31,40.0– 49.4 mm SL, India: Uttar Pradesh, Saharanpur, Padhoe River at Kalsia Ghat, Ganga River basin, K.P. Singh, 20 January 1972. RGUMF, unregistered, 3, 45.2–55.5 mm SL, India: Uttarakhand, Nainital district, Gola River at Kathgodam, Ganga River basin, A. Darshan, 30 April 2011. MUMF 14301–14302, 2, 35.5–37.1 mm SL, India: Barak River at Silchar (Assam), M. Shantakumar and K. Nebeshwar, 16 December 2000. MUMF 14061, 1, 48 mm SL, India: Arunachal Pradesh, Dikrong River, K. Nebeshwar.

Amblyceps arunachalensis: RGUMF 117, 82.6–97.2 mm SL, 3, India: Arunachal Pradesh, Subansiri River at Daporijo, Brahmaputra basin, 7 June 2005.

Amblyceps apangi (S4 Table): RGUMF 118, 160.0 mm SL, India, Arunachal Pradesh, Papum Pare district, Dikrong River at Sagalee, Brahmaputra basin, 7 January, 2005. RGUMF 114, 45–91.2 mm SL, 7, India, Arunachal Pradesh, Papum Pare district, Dikrong River, Brahmaputra basin, 17 July 2005. RGUMF 116, 71.5 –120.0 mm SL, 7, India, Arunachal Pradesh, Subansiri River at Daporijo, Brahmaputra basin, 7 June 2005.

A. torrentis: MUMF 6170, 85.0 mm SL, holotype, India, Manipur, Ukhrul district, Laniye River at Jessami village, Chindwin basin. MUMF 2111, 1, 76.8 mm SL, paratype, India: Manipur, Ukhrul district, Challou River at Chingai village, Chindwin basin. Additional data from Linthoingambi and Vishwanath [10].

A. tuberculatum: MUMF 6184, holotype, 97.2 mm SL, India: Manipur, Chandel district, Lokchao River at Moreh town, Chindwin basin. MUMF 6179–6180, 69.4–76.3 mm SL, 2, paratype, same data as above. Additional data from Linthoingambi and Vishwanath [10].

A. platycephalus, A. variegatum, A. foratum, and A. serratum: Data from Ng and Kottelat [9].

A. caecutiens, A. kurzii, A. protentum, A. laticeps, and A. murraystuarti: Data from Ng and Wright [4], and Ng and Kottelat [9].

A. tenuispinis and A. cerinum: Data from Ng and Wright [1].

A. carinatum: Data from Ng [11].

A. macropterus: Data from Ng [12].