Physoschistura walongensis, Tamang, Lakpa & Sinha, Bikramjit, 2016

Tamang, Lakpa & Sinha, Bikramjit, 2016, Physoschistura walongensis, a new species of loach (Teleostei: Nemacheilidae) from Arunachal Pradesh, northeastern India, Zootaxa 4173 (3), pp. 280-288 : 281-285

Physoschistura walongensis , sp. nov.

( Fig. 1 )

Type material. Holotype. ZSI/ APRC 1190, 50.5 mm SL, male; India: Arunachal Pradesh: small diverted water course of Lohit River (Brahmaputra River basin) at Walong ; 28°07.395ʹ N, 97° 01.096ʹE, 1096m asl, B. Sinha and L. Tamang, 29 November 2014.

Paratypes. ZSI/APRC 1268, 1 specimen, 45.4 mm SL, male; ZSI/APRC 1269, 12 specimens, 42.0– 56.4 mm SL (4 males + 8 females); ZSI/APRC 1270,5 specimens, 44.1–55.1 mm SL (skeleton: 3 males + 2 females); other data are same as for holotype.

Diagnosis. The new species is distinguished from its congeners by the following combination of characters: an incomplete lateral line reaching at least to vertical through the anal-fin origin and maximally to vertical through tip of adpressed anal fin, with 71–89 canal pores; a rounded suborbital flap, the posterior margin of which slightly exceeds the anterior orbital margin, occupying less orbital area; body with 11–18 irregular vertical bars on the flank, more irregular on anterior portion of the body; 1–4 bars bifurcate ventrally; 1–4 saddles along the ventrolateral side of the body; a moderately thick W-shaped basicaudal bar; a prominent axillary pelvic fin lobe; dark brown mottled markings on the head; lips pleated; and forked caudal fin with 9 upper + 8 lower branched rays.

Description. For general appearance see Figure 1 . Morphometric data are presented in Table 1 and meristic data in Table 2 . Body elongate (depth 13.8–16.9% SL), not greater than 56.4 mm SL, anterior body between pectoral fin and dorsal-fin origins cylindrical, gently compressed to anal-fin origin and thereafter greatly decreasing to caudal-fin base; body deepest at pectoral-fin origin or just posterior to it. Predorsal profile almost evenly rising from snout tip to dorsal-fin origin except slight depression on occipital margin, postdorsal body sloping gently ventrally to anterior base of adipose crest and then very slightly increasing to caudal-fin base.Ventral profile almost flat to anal-fin origin, slightly rising to anterior base of adipose crest and then very gently rising to caudal-fin base.

Head moderate, triangular when viewed laterally and broader than high, lateral head length (22.1–25.5% SL) longer than dorsal (18.2–21.9 % SL). Snout obtusely pointed; mouth inferior and strongly arched, 1.4–1.6 times wider than long. Lips fleshy, feebly pleated, continuous around corner of mouth. Lower lip with two large roughly triangular pads separated by extremely narrow median interruption, anterior mouth gap diamond-shaped. Median notch on lower jaw absent. Three pairs of barbels: one pair maxillary and two pairs rostral —inner rostral barbel shortest, extending to base of maxillary barbel; outer rostral barbel longest (slightly longer than maxillary barbel) and almost reaching posterior orbital margin; maxillary barbel extending beyond posterior orbital margin or halfway between its base and pectoral-fin origin. Eye moderate, invisible ventrally, situated slightly closer to snout tip than to posterior extremity of opercle, separated by moderately broad interorbital space. Suborbital flap broadly rounded and posteroventrally directed, posterior margin slightly exceeding anterior orbital margin, occupying less orbital area ( Fig. 3 a). Nostril closer to eye than to tip of snout, nares separated by small membrane flap dividing nostril into two parts; anterior nare tubular, attached with membrane flap; posterior nare slightly larger than anterior, separately situated posterior to base of membrane flap. Anus situated very close to anal-fin origin. Intestine coiling includes a loop just behind stomach ( Fig. 4 ).

Body embedded with minute scales, absent on ventral surface between isthmus and anal-fin origin. Lateral line incomplete, extending between anal-fin origin and its tip with 71–89 pores. Flank with 11–18 vertical bars, bars more irregular on anterior portion of body,1–2 bars sometimes branched and inversely U-shaped; interspaces mostly narrower than bars; 1–4 saddles on ventrolateral side, absent dorsolaterally. Head sensory pores consisting of 4+9–10 infraorbital pores, 9–10 supraorbital pores, 3 occipital pores, 8–9 preoperculomandibular pores (not distinctly visible). Vertebrae in 5 specimens 37–39.

Dorsal fin with 4 simple and 8½ rays, situated at vertical slightly in front of pelvic-fin origin and nearer to caudal-fin base than to snout tip; tip of last ray at vertical to anal-fin tip, anterior and posterior margins straight and distally slightly arched, first or second branched ray longest. Pectoral fin broadly leaf-shaped, tip pointed, with 1 simple and 9–10 branched rays, second or third branched ray longest, anterior margin slightly convex and posterior straight to gently arched. Pelvic fin with 1 simple, 6–7 branched rays, its shape similar to pectoral fin, tip never reaching anus but closer to anal-fin origin than to base of last pectoral-fin ray. Anal-fin with 4 simple and 5 branched rays, anterior margin slightly convex and posterior straight, not reaching hypural margin but touching last vertical bar on body. Caudal fin forked with 9 upper + 8 lower branched rays, lobes mostly subequal, lower lobe longer than upper. Caudal peduncle 1.2–1.6 times longer than deep, with low dorsal and ventral adipose crests on posterior half.

Dorsal-fin rays (simple/branched) iv,8,i

Pectoral-fin rays (simple/branched) i,9,i (9)/ i,10,i(4)/ i,10,ii * (6) Pelvic-fin rays (simple/branched) i,6,i * (10)/ i,7 (3)/ i,7,i (6) Anal-fin rays (simple/branched) iv,5,i * (8)/ iv,5 (11) Caudal-fin rays (upper/lower lobes) i,9,8,i

Vertebrae (5 specimens) 37–39

Lateral-line canal pores 71–89

Vertical bars on body 11(2)/ 13(5)/14(5)/ 15(5)/16 * (1)/ 18(1) Color in preservative. In 10% formalin, body background light yellowish cream with light grayish brown bands. Dorsum of head with small round to elongate irregular light grayish brown marks, much smaller than bars on body. Lips and barbels white-cream except outer rostral barbel light brown dorsally. Ventral surface of head and along ventrolateral area to caudal-fin base light yellowish cream. Isthmus and abdominal region white-cream. Dorsal fin with one dark brown spot at origin, indistinct faint brown band along middle; sometime entirely hyaline. Pectoral fin with 5–7 anterior rays light brown, distinctiveness decreasing posteriorly and distally, ventral base with light yellowish tinge; others hyaline. Pelvic and anal fins entirely hyaline except light yellowish tinge at base ventrally. Caudal fin light brown to dusky, without bands.

Sexual dimorphism. Specimens with subortibal flap presumed to be males ( Kottelat, 1984). In the type series are 8 males (42.0– 54.7 mm SL) and 11 females (44.0– 56.4 mm SL), potentially pointing to a small difference in size between sexes.

Habitat. The new species was collected from the right bank of the Lohit River in shallow water (ca. 10–20 cm depth) at Walong ( Figs. 5 and 6 ). The substrate was a mixture of pebbles, cobbles, small stones of variable colors in pools, and the surrounding area with moderate-sized boulders irregularly placed, and heavy sand deposits along the bank. The water was moderate to fast flowing, cool, and clear in a container, but light greenish in the river. The river is bordered by high mountains throughout, with pine and other small trees and shrubs. Other fishes collected at this locality belong to genus Schizothorax, Garra , and Creteuchiloglanis .

Distribution. Physoschistura walongensis is known only from the type locality in the Lohit River, Walong, Anjaw district ( Fig. 5 ).

Etymology. The specific name is derived from the name of the area (Walong) from where the new species was obtained.

Figures

FIGURE 3. Suborbital flap: a, Physoschistura walongensis, paratype, ZSI / APRC 1269, 45.4 mm SL, male; b, P. dikrongensis, holotype, MUMF 11091 / 3, 44.6 mm SL, male, showing extension of posterior margin of suborbital flap.

FIGURE 4. Physoschistura walongensis, ZSI / APRC 1270, paratype, 50.1 mm SL; digestive tract. Scale bar = 1 mm.

FIGURE 5. Faroff view of Lohit River at Walong showing the type locality of Physoschistura dikrongensis (indicated by arrow).

FIGURE 6. Map of Arunachal Pradesh, northeastern India, showing the type localities of Physoschistura walongensis (filled circle) and P. dikrongensis (filled square).

FIGURE 1. A and b, Physoschistura walongensis, holotype, ZSI / APRC 1190, 50.5 mm SL, male; c and d, paratype, ZSI / APRC 1269, 56.4 mm SL, India, Arunachal Pradesh.

Tables

TABLE 2. Meristic data of Physoschistura walongensis (19 specimens).

	Holotype	Range	Mean±SD
Standard length(mm)	50.5	42.0–56.4	48.2±4.0
Body depth	14.9	13.8–16.9	15.5±0.9
Head depth at eye	10.2	10.5–12.9	11.6±0.7
Dorsal head length	20.6	18.2–21.9	20.1±1.1
Lateral head length	23.1	22.1–25.5	23.9±0.9
Caudal-peduncle length	12.9	12.3–15.7	13.7±0.9
Caudal-peduncle depth	9.6	9.0–11.5	10.3±0.7
Upper caudal lobe length	21.8	18.7–23.2	21.0±1.2
Lower caudal lobe length	22.1	19.9–25.5	22.2±1.6
Median caudal ray	15.0	13.4–17.8	15.4±1.2
Predorsal length	52.4	49.8–54.4	52.4±1.1
Prepelvic length	52.9	52.6–56.4	54.5±1.2
Preanus length	75.7	75.3–80.4	76.9±1.3
Preanal length	80.4	76.2–83.4	79.8±1.4
Dorsal-fin length	15.0	14.6–16.2	15.3±0.5
Anal-fin length	15.5	14.0–17.3	15.8±0.9
Pectoral-fin length	18.6	18.2–21.7	19.6±0.9
Pelvic-fin length	15.9	15.5–17.5	16.6±0.7
Maximum head width	13.7	13.6–15.5	14.7±0.6
Head width at nares	9.2	9.2–11.3	10.1±0.7
Body width at dorsal-fin origin	11.6	10.5–14.1	12.5±0.9
Body width at anal-fin origin	7.0	6.6–9.0	8.0±0.7
%Lateral head length
Snout length	42.8	34.4–42.4	39.4±2.4
Interorbital distance	32.7	24.5–31.5	28.0±2.1
Eye diameter	17.8	11.4–19.3	15.1±2.0
Mouth length	25.3	21.8–32.5	26.6±2.7
Mouth gape width	35.8	33.0–48.8	40.1±3.7
Maximum head width	63.0	56.0–66.8	61.1±3.0
Head width at nares	42.5	37.8–49.0	40.8±3.2
Ratios
Lateral/dorsal head depth	1.1	0.6–1.3	1.2±0.1
Body depth/width	1.2	1.1–1.6	1.2±0.1
Caudal-peduncle length/depth	1.5	1.2–1.6	1.3±0.1
Mouth gape width/length	1.4	1.4-1.6	1.5±0.1