Physoschistura harkishorei, Das & Darshan, 2017

Das, Debangshu Narayan & Darshan, Achom, 2017, Physoschistura harkishorei, a new species of loach from Arunachal Pradesh, north-eastern India (Teleostei: Nemacheilidae), Zootaxa 4337 (3), pp. 403-412 : 404-409

Physoschistura harkishorei , new species

( Fig. 1 )

Holotype. RGUMF 290 , 41.3 mm SL; male, India: Arunachal Pradesh state, Lower Dibang Valley district, Dibang River (the Brahmaputra basin); 28°09´59˝ N 95°43´55˝E; Boni Amin Laskar , August 2004.

Paratypes. RGUMF 291–295, 5, 42.5–53.4 mm SL; same data as holotype. RGUMF 332 , 1 , 46.1 mm SL, male, India: Arunachal Pradesh state, Lohit district, Lohit River at Alubari Ghat , at the immediate side of Lohit bridge ( Alubari bridge), 27°51´29˝ N 96°01´36 ˝ E, elevation 159 msl; Achom Darshan and Santoshkumar Abujam , 29th August 2016 .

Diagnosis. Physoschistura harkishorei can be distinguished from all known congeners by the combination of the following characters: the second branched ray of the pectoral fin with a distal filamentous extension; body colour pattern consisting of 9–10 brownish vertically-elongated spots or blotches along the flank, 8–10 brownish saddles on back, saddles not contiguous with the lateral blotches; lateral line complete; a pelvic-fin lobe present; a well-developed free posterior chamber of the air-bladder; and caudal fin with 7+8 branched rays.

Description. Morphometric data of holotype and six paratypes are shown in Table 1 . Dorsal profile elevating abruptly in snout region, gently inclined to dorsal-fin origin, then sloping gently downwards towards caudal fin; ventral profile almost straight up to anal-fin origin, then inclined evenly towards caudal-fin base. Body crosssection sub-cylindrical anteriorly, laterally compressed from base of last pectoral-fin ray to base of caudal fin. Body covered with minute scales, absent between bases of pectoral fin and belly anterior to pelvic fin. Lateral line midlateral, complete, and straight. Cephalic lateral-line system with 7 supraorbital, 4 + 11 infraorbital, 9 preoperculo-mandibular, and 3 supratemporal pores.

Head depressed. Eye oval, placed in upper and anterior half of head, not visible in ventral view. Interorbital space flat, wide. Mouth inferior, small, strongly curved backward, about twice as wide as long. Processus dentiformis present, no corresponding notch in lower jaw. Lower lip with prominent median notch, forming two triangular pads ( Fig. 2 ). Three pairs of barbels, outer rostral barbel long, reaching posterior rim of eye; inner rostral barbel shorter, extending to middle of snout; maxillary barbel extending slightly beyond vertical through posterior rim of eye. Anterior and posterior nostrils adjacent. Anterior nostrils in a flap-like tube, its tip truncate.

Dorsal fin with 2(2) or 3*(5) simple and 8(1) or 8½*(5) or 9(1) branched rays, its origin slightly anterior to vertical through pelvic-fin origin. Distal margin of dorsal fin slightly convex. Pelvic fin with 1(7) simple and 7(7) branched rays. Pelvic-fin lobe prominent and large. Pectoral fin with 1(7) simple and 9 (1) or 10 *(6) branched rays. Second branched ray of pectoral fin with distal filamentous extension, often extended far beyond pelvic-fin origin, reaching upto posterior margin of pelvic-fin lobe in larger specimens greater than 49.0 mm SL. Anal fin with 2(7) simple and 5 (1) or 5½* (6) branched rays. Adpressed pelvic fin not reaching vent. Caudal fin forked, lobes equal in length, with 7+8 branched rays. Free posterior chamber of air-bladder placed immediately behind air-bladder capsule, spherical in shape, not encapsulated ( Fig. 3 ). Intestine with large loop extending forward towards left posterolateral side of stomach ( Fig. 4 ).

Sexual dimorphism. Males possess a suborbital flap ( Fig. 5 ) while females have a suborbital groove in place of male’s suborbital flap. The first branched pectoral-fin ray broadens in males by fusing together and separating at towards the tip ( Fig. 6 ). No distinct sexual dichromaticism or dimorphism.

Colouration. In 70% alcohol, background body colour yellowish cream, ornamented dorsally with 8–10 brownish saddles and 9–10 vertically elongated spots or blotches along flank, saddles alternately placed with lateral blotches, not contiguous. In some paratypes, predorsal lateral blotches extend well below lateral line. Head and snout region scattered with brown spots. A conspicuous dark-brown spot at dorsal-fin origin, a transverse brownish streak at middle of dorsal fin due to heavy accumulations of melanophores in mid-region of fin rays. Mid-base of dorsal fin, from third to sixth branched rays, along with the adjoining basal membrane brownish, distal and sub-basal portion of dorsal fin hyaline. Basicaudal bar basally broad, narrower dorsally, incomplete, terminated at a point about half eye diameter above ventral margin of caudal-fin base.

Etymology. The new species is named in memory of Late Harkishore Das, the father of the first author, who inspired him (DND) to take up fisheries research as his academic career.

Distribution. Presently, known from the Dibang River, its type locality and the Lohit River (both Brahmaputra basin) in Arunachal Pradesh ( Figs. 7 , 8 ).

Discussion

Physoschistura harkishorei differs from P. dikrongensis , and P. elongata , its sympatric congeners in the Brahmaputra basin, in having a complete (vs. incomplete) lateral line, a filamentous extension (vs. lacking extension) in the second branched ray of the pectoral fin, and lateral body markings in the form of verticallyelongated blotches (vs. bars). Further, P. harkishorei differs from P. dikrongensis by its shorter snout (32.9–40.6% HL vs. 44.1–53.9), dorsal-fin (9.1–10.4% SL vs. 13.8–17.7), 8–10 blotches (vs. 11–15 bars) along the flank, fewer (2 vs. 4) simple anal-fin rays, and supraorbital canal pores (7 vs. 9); and from P. elongata in having a longer caudal peduncle (12.9–16.7% SL vs. 11.3) and a shorter prepelvic length (46.8–53.2% SL vs. 53.8).

The new species differs from P. chhimtuipuiensis in having a complete (vs. incomplete) lateral line, a filamentous extension (vs. lacking extension) of the second branched ray of the pectoral fin, a shorter head (lateral head length 19.4–22.8% SL vs. 23.0–25.9, dorsal head length 17.6–19.3% SL vs. 21.5–22.7), snout (32.9–40.6% HL vs. 42.0–45.0), a slender caudal peduncle (6.8–8.7% SL vs. 10.9–12.1), a narrower interorbital distance (21.2– 25.5% HL vs. 29.0–32.0) and absence (vs. presence) of scales between bases of pectoral-fin and on the belly.

The new species and Physoschistura raoi are the only two members of the genus with a long pectoral fin extending up to the origin of the pelvic fin. In the new species, the pectoral fin is extended to the pelvic-fin origin or often beyond by means of a distal filamentous extension of the second branched ray ( Figs. 9a & b ). In case of P. raoi , the pectoral fin is large and long but lacking any filamentous extension of the fin rays ( Fig. 9c ). Further, the new species differs from P. raoi by its complete lateral line (vs. incomplete).

The new species can be easily distinguished from P. rivulicola , P. chulabhornae , P. pseudobrunneana , and P. brunneana in having a complete (vs. incomplete) lateral line and the second branched ray of the pectoral fin filamentously extended (vs. lacking filamentous extension). It further differs from P. chulabhornae , P. pseudobrunneana , and P. brunneana in having (vs. lacking) a pelvic-fin lobe.

Physoschistura harkishorei shares with P. tuivaiensis , P. chindwinensis , P. prashadi , P. tigrina , P. shanensis , P. shuangjiangensis and P. absumbra a complete lateral line; but is distinct from them by having (vs. lacking) a filamentous extension of the second branched ray of the pectoral fin. Further, P. harkishorei differs from P. tuivaiensis and P. chindwinensis in having a shorter snout (32.9–40.6% HL vs. 43.4–51.0) and head (lateral head length 19.4–22.8% SL vs. 23.1–27.3); from P. prashadi by its fewer (2–3 vs. 4) simple dorsal-fin rays, shorter snout (32.9–40.6% HL vs. 43.8–57.0), and narrower interorbital distance (21.2–25.5% HL vs. 28.2–40.1); from P. tigrina by its shorter snout (32.9–40.6% HL vs. 46.9–50.6), more slender body (13.3–15.9% SL vs. 17.0–19.0), caudal peduncle depth (6.8–8.7% SL vs. 9.8–11.0), and narrower interorbital distance (21.2–25.5% HL vs. 27.3– 29.2); from P. shanensis in having fewer branched pectoral-fin rays (9–10 vs. 12) and branched caudal-fin rays in the upper lobe (7vs. 8); from P. shuangjiangensis by its slender body (head depth at nape 11.3–13.4% SL vs. 13.9– 15.2, body depth 13.3–15.9% SL vs.17.9–20.5, caudal peduncle depth 6.8–8.7% SL vs. 11.0–13.1) and fewer branched caudal-fin rays in the upper lobe (7 vs. 9), and from P. absumbra in having an incomplete (vs. complete) basicaudal bar, a shorter head (dorsal head length17.6–19.3% SL vs. 23–25, lateral head length19.4–22.8% SL vs. 26–28), and a body colour pattern consisting of vertically elongated lateral spots or blotches (vs. regular bars).

Figures

FIGURE 1. Physoschistura harkishorei, holotype, RGUMF 290, 41.3 mm SL: a. lateral; b. dorsal; c. ventral view.

FIGURE 2. Lip structure of Physoschistura harkishorei: a. RGUMF 291, paratype, 53.4 mm SL; b. RGUMF 290, holotype, 41.3 mm SL.

FIGURE 3. Ventral view of air bladder of Physoschistura harkishorei, RGUMF 295, 43.4 mm SL, showing free posterior chamber (not to scale) [pc: posterior chamber].

FIGURE 4. a & b. Intestine coiling of Physoschistura harkishorei, RGUMF 291, paratype, 51.6 mm SL. [scale bar 5 mm].

FIGURE 5. Head of Physoschistura harkishorei, showing a suborbital flap of male, RGUMF 290, holotype, 41.3 mm SL.

FIGURE 6. Pectoral fin of Physoschistura harkishorei: a. male, RGUMF 290, holotype, 41.3 mm SL; b. female, RGUMF 291, paratype, 53.4 mm SL [br 1: first branched ray, fpbr 2: filamentous extension of second branched ray].

FIGURE 7. Map of Arunachal Pradesh showing the distribution of Physoschistura harkishorei, new species (triangle: Dibang River at Roing, Circle: Lohit River at Alubari) (redrawned from Darshan et al. 2016).

FIGURE 8. Photograph showing the habitat of Physoschistura harkishorei in the Lohit River (viewing towards the southern bank at the side of Alubari Bridge).

FIGURE 9. Pectoral fin: a & b. Physoschistura harkishorei, RGUMF 291, paratype, 53.4 mm SL; (c) Physoschistura raoi (reproduced from Hora 1929, Plate 15, Fig. 7).

Tables

TABLE 1. Morphometric data of Physoschistura harkishorei, new species (n = 7).

	Holotype	Range	Mean ± SD
Total length (mm)	51.7	51.7–63.2	-
Standard length (mm)	41.3	41.3–53.4	-
In percent of standard length
Body depth	13.4	13.3–15.9	14.7±1.23
Head depth at nape	12.3	11.3–13.4	12.3±0.75
Head depth at eye	10.4	8.5– 11.4	9.8±1.19
Lateral head length	22.8	19.4–22.8	21.4±1.27
Dorsal head length	19.2	17.6– 19.3	93.8±0.72
Caudal peduncle length	15.9	12.9–16.7	75.1±1.47
Caudal peduncle depth	7.7	6.8–8.7	38.6±0.88
Pre-dorsal length	50.8	44.2–50.8	236.7±2.41
Pre-pelvic length	49.2	46.8–53.2	251.7±2.44
Pre-anus length	68.8	66.7–71.7	342.9±1.91
Pre-anal length	75.5	73.2–76.7	377.6±1.41
Pelvic fin length	16.5	14.9–17.4	80.7±0.92
Anal fin length	17.7	15.1–17.8	81.4±1.34
Pectoral fin length	26.9	23.1–28.9	133.8±2.38
Maximum head width at cheek	9.9	9.9–12.2	56.8±0.89
Head width at nares	7.5	7.5–10.5	43.4±1.12
Body width at anal-fin origin	6.3	6.3–8.0	36.5±0.69
Body width at dorsal-fin origin	9.7	9.5–12.9	53.9±1.36
In percent of lateral head length
Snout length	32.9	32.9–40.6	188.3±3.13
Interorbital distance	25.5	21.2–25.5	121.4±1.79
Eye diameter	25.5	21.2–26.7	117.7±2.48
Mouth gape width	29.8	23–33.7	141.9±3.96
Head depth at eye	45.7	38.3–50.0	227.1±4.39
Head depth at nape	54.3	51.6–62.7	284.6±4.23
Maximum head width	43.6	5.6–59.3	213±6.11