Schistura notostigma ( Bleeker, 1863 )

Sudasinghe, Hiranya, 2017, Schistura madhavai, a new species of hill-stream loach from Sri Lanka, with redescription of S. notostigma (Teleostei: Nemacheilidae), Zootaxa 4311 (1), pp. 96-110 : 104-106

Schistura notostigma ( Bleeker, 1863)

( Figure 8 )

Material examined. All from Sri Lanka: DZ 3756 (3), 34.2–38.7 mm SL, Attanagalu River basin, Wahareka. DZ 3620 (2), 40.4–41.5 mm SL, Kelani River basin, Deraniyagala. WHT 30034 (2), 27.7–33.2 mm SL, Kelani River basin, Heen ela, Waga . WHT 30457 (2), 32.5–34.7 mm SL, Kelani River basin, Wak Oya, Kahahena. DZ 3420 (3), 31.2–35.7 mm SL, Kalu River basin, Malwara Forest reserve, Halwala. DZ 3368, 42.7 mm SL, Kalu River basin, Malwara Forest reserve, Halwala. DZ 3421 (3), 38.3–46.6 mm SL, Kalu River basin, Kukuleganga south, Kalawana. DZ 3462 (3), 31.1–39.6 mm SL, Kalu River basin, Athwelthota. DZ 3422 (4), 26.1–33.7 mm SL, Kalu River basin, Athwelthota. DZ 3419 (3), 38.7–41.2 mm SL, Kalu River basin, Padukka. WHT 120 (4), 42.2–47.4 mm SL, Kalu River basin, Walandure, Kuruwita . WHT 30491 (4), 34.6–43.5 mm SL, Kalu River basin, Koskulana, Panapola. DZ 3424 (2), 30.8–33.5 mm SL, Bentara River basin, Pitigala . WHT 30218 (2), 29.2–33.4 mm SL, Gin River basin, Kottawa, Galle. WHT 2010 (3), 29.5–40.6 mm SL, Gin River basin, Kottawa forest reserve, Galle . WHT 30668 (4), 27.0– 33.6 mm SL, Gin River basin, Udugama ela. DZ 3589 (6), 26.3–39.8 mm SL, Mahaweli River basin, Peradeniya, Kandy. DZ 3417 (5), 42.6–51.8 mm SL, Mahaweli River basin, Peradeniya, Kandy . WHT 30629 (3), 49.1–63.1 mm SL, Mahaweli River basin, Paradeka, Pussellawa. WHT 38 (5), 41.9–54.9 mm SL, Mahaweli River basin, Mousakanda, Gammaduwa, Knuckles.

Diagnosis. Schistura notostigma is distinguished from all peninsular-Indian and Sri Lankan congeners by the combination of the following characters: 6–7 wide, brown bars on the posterior half of the body; the width of interspaces equal ½–1 times the width of the bars; the black bar on caudal-fin base complete, narrower than the width of the interspaces on the body; an emarginate caudal fin; an incomplete lateral line ending beneath the dorsal-fin base; the adpressed pelvic fin surpassing the anus; dorsal fin with 7½ branched rays, origin of pelvic fin beneath first branched dorsal-fin ray; 4–8 pre-operculo-mandibular pores; and the absence of suborbital flap in males.

Description. General appearance as in Figure 8 ; morphological data provided in Table 2. A medium-sized Schistura , up to 63.1 mm SL. Body moderately deep, slightly compressed anteriorly, moderately compressed posteriorly. Maximum body depth between origin of dorsal fin and distal margin of adpressed pectoral fin. Body depth almost constant from origin of dorsal fin to base of caudal fin. Head slightly depressed. Dorsal head length and lateral head length greater than head width. Snout rounded in dorsal and lateral view. Eyes small, located dorsolaterally, not visible ventrally. Depth of caudal peduncle 0.7–0.9 times its length. Caudal peduncle with small dorsal adipose crest, originating just anterior to vertical through anal-fin origin, reaching caudal-fin origin. Ventral adipose crest originating posterior to base of anal fin, reaching caudal-fin base. No axillary pelvic lobe in most populations.

Dorsal fin with its origin at or slightly anterior to vertical through origin of pelvic fin, with four simple and 7½ (22) branched rays. Tip of adpressed dorsal fin just reaching vertical through origin of anal fin. Anal fin with three simple and 5½ (21) branched rays. Anal fin not reaching caudal-fin base. Caudal fin emarginate, with 8+8 (20) or 8+7 (2) branched rays; lobes rounded, of equal length. Pelvic fin with one (22) simple and six (22) branched rays, reaching half-way to anal fin, surpassing anus; origin beneath first branched dorsal-fin ray. Pectoral fin with one (22) simple and eight (19) or nine (3) branched rays, reaching slightly beyond half-way to pelvic fins. Distal margins of dorsal, anal and pelvic fins convex.

Lateral line incomplete, reaching origin of dorsal fin or slightly beyond, with 22–52 pores. Body entirely scaled, more prominent in sub-dorsal and post-dorsal region. Body anterior to dorsal-fin origin usually with minute, less prominent scales, absent in some populations. Cephalic lateral line system with 6–9 supraorbital, 4+6– 9 infraorbital, 4–8 pre-operculo-mandibular and 3 supratemporal pores.

Mouth, large, inferior, curved. Lips thick; upper lip with slight median incision; lower lip with deep medial interruption. Both lips with furrows along entire length, furrows more prominent in lower lip ( Fig. 3 B). Processus dentiformis present, wide, rounded. Anterior nostril tubular, pierced anteriorly, terminating in an elongate flap ( Fig. 4 B). Inner rostral barbel just reaching vertical through nostrils; outer rostral barbel ending between verticals through anterior and posterior margins of eye; maxillary barbel extending just beyond vertical through preoperclar margin. Suborbital flap absent.

No apparent sexual dimorphism.

Coloration. In 70% alcohol ( Fig. 8 B): adults (> 30 mm SL) with head and body brown dorsally, light brown laterally, creamish-white ventrally. Head darker than body. Rostral barbels with greyish-brown pigments; maxillary barbels creamish white. Pre-dorsal bars absent, or present as 3–4 brown bars separated by light brownish cream interspaces. Post-dorsal bars 6–7, brown, width approximately ½–1 times eye diameter. Width of interspaces between bars ½–1 times width of bars. Some interspaces bifurcated laterally and some coalescing along dorsal mid line. Black bar at caudal-fin base complete, its width distinctly less than interspaces on body. Pectoral, pelvic and anal fins hyaline. Black spot at dorsal-fin origin, with smaller, less distinct spot behind it, along base of dorsal fin. Two rows of distinct black spots on rays of dorsal fin. Interradial membrane of dorsal fin with no distinct melanophores. Two or three rows of black spots on rays of caudal fin.

In life ( Fig. 8 C): adults (> 35 mm SL) with dark-brown bars and light-brown interspaces of width as in preserved specimens. Anterior region of rostral barbels tinged light orange, remainder light brown. Maxillary barbels light brown. Black bar at caudal-fin base complete, distinctly narrower than interspaces on body. Pectoral, pelvic and anal fins with light-yellow pigmentation on rays. Rays of caudal and dorsal fins yellowish orange. Black spot at dorsal-fin origin, with smaller, less distinct one behind it, straddling the bases of branched rays 3–5. Two rows of distinct black spots on rays of dorsal fin. Two or three rows of black spots on rays of caudal fin.

Habitat and distribution. Schistura notostigma prefers fast flowing streams with a rock or pebble substrate. The species is widely distributed in the southwest quadrant of Sri Lanka, occurring in streams descending from the hills. I have not recorded it however, from the coastal floodplain and hill streams above an elevation of about 1300 m ( Fig. 6 B).

Figures

FIGURE 3. Mouth of A, Schistura madhavai (2017.02.01. NH) and B, S. notostigma (DZ 3462). Scale bar 1 mm.

FIGURE 4. Left nostril of A, Schistura madhavai (2017.02.01. NH) and B, S. notostigma (WHT 30668). Scale bar 2 mm.

FIGURE 6. A, Habitat of Schistura madhavai: Suriyakanda, Sri Lanka; B, Distribution of S. madhavai (red) and S. notostigma (black) in Sri Lanka, based on material examined in this study.

FIGURE 8. A, Nemacheilus notostigma, reproduced from Bleeker (1864: 5, pl. 1 fig. 2); B, Schistura notostigma (DZ 3462 C, 35.3 mm SL), Sri Lanka, Kalu basin, Athwelthota; C, coloration in life of adult S. notostigma in natural habitat (~ 45 mm SL, not preserved), Sri Lanka, Attanagalu Oya basin, Wahareka.