Schistura madhavai, Sudasinghe, 2017

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 : 98-104

Schistura madhavai , sp. nov.

( Figures 1 , 2 )

Holotype: 2017.02.01.NH, 49.7 mm SL; Sri Lanka, Walawe River basin, Suriyakanda, 6°27'02"N 80°37'01"E, 1000 m asl. H. Sudasinghe. Nov 2015.

Paratypes: 2017.03.01.NH, 55.3 mm SL, same data as holotype. 2017.03.02.NH, 45.8 mm SL, Sri Lanka, Walawe River basin, Suriyakanda, 6°27'02"N 80°37'01"E, 1000 m asl . H. Sudasinghe. Jul 2016. DZ 3418C, 51.2 mm SL, same data as holotype. DZ 3458 (3), 34.8–44.2 mm SL, Sri Lanka, Walawe River basin, Suriyakanda, 6°27'02"N 80°37'01"E, 1000 m asl . H. Sudasinghe, Jul 2016.

Diagnosis. Schistura madhavai is distinguished from all peninsular-Indian and Sri Lankan congeners by the combination of the following characters: 8–9 wide post-dorsal bars separated by narrow, white interspaces ¼–⅓ the width of the bars; the black bar at the base of the caudal fin arched, its posterior margin vaguely indented at bases of branched caudal-fin rays 3 and 14, wider than the interspaces on the body; an emarginate caudal fin with 8+8 branched rays; an incomplete lateral line ending beneath the dorsal-fin base; the absence of an axillary pelvic lobe; the adpressed pelvic fin just reaching the anus; the dorsal fin with 7½ branched rays; the origin of the pelvic fin on a vertical through the last unbranched dorsal fin ray; and the absence of a suborbital flap in males.

Description. General appearance as in Figures 1 , 2 and 5 ; morphological data provided in Table 2. A mediumsized Schistura , up to 55.3 mm SL. Body 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 0.8–0.9 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.

Dorsal fin with its origin at or slightly anterior to vertical through origin of pelvic fin, with four simple and 7½ (7) branched rays. Tip of adpressed dorsal fin ending just before vertical through origin of anal fin. Anal fin with three simple and 5½ (7) branched rays. Anal fin not reaching caudal-fin base. Caudal fin emarginate, with 8+8 (7) branched rays; lobes rounded, of equal length. Pelvic fin with one (7) simple and six (7) branched rays, reaching half-way to anal fin, just reaching anus; origin beneath last unbranched dorsal-fin ray. Pectoral fin with one (7) simple and eight (6) or nine (1) 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 27–53 pores. Body entirely scaled except region anterior to dorsal-fin origin. Body scales on sub-dorsal region smaller than those on postdorsal region. Cephalic lateral-line system with 6–7 supraorbital, 4+7–9 infraorbital, 9–10 pre-operculomandibular 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, more pronounced medially ( Fig. 3 A). Processus dentiformis present, wide, rounded. Anterior nostril a low flap-like pointed tube, pierced on anterior side ( Fig. 4 A). Inner rostral barbel just reaching vertical through nostril; outer rostral barbel ending between verticals through anterior and posterior margins of eye; maxillary barbel extending just beyond vertical through preopercular margin. Suborbital flap absent.

No apparent sexual dimorphism.

Coloration. In 70% alcohol ( Figure 2 ): large adults (> 45 mm SL) with head and body greyish-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 only as 1–2 poorly-contrasted brown bars separated by narrow, lighter interspaces. Post-dorsal bars brown, 8–9, width about equal to 1½ times eye diameter. White interspaces between bars narrow, ¼–⅓ times bar width. Some interspaces bifurcated ventrally, some coalescing along dorsal midline. Post-dorsal bars in some specimens with incomplete interspaces (not extending to dorsal or ventral surfaces: see Fig. 5 A). Black bar at caudal-fin base not reaching dorsal or ventral midline, wider than white interspaces on body, arched, its posterior margin vaguely indented at bases of branched caudal-fin rays 3 and 14. Pectoral, pelvic and anal fins hyaline. Holotype with horizontally elongate black blotch about as wide as eye diameter along dorsal-fin base, darker anteriorly, becoming lighter posteriorly. In larger paratypes (2017.03.01.NH and DZ 3418C), black blotch at origin of dorsal fin present, followed by dull yellow mark along fin base and black line above dull-yellow mark on fin. In smaller paratypes (2017.03.02.NH and DZ 3458 A, C, D) black blotch only at origin of dorsal fin, prominent. Dorsal and caudal fin rays with dense aggregations of melanophores along their length. Melanophores distributed medially along interradial membranes of dorsal fin. Patterning of melanophores on dorsal fin more prominent in large specimens than in smaller ones.

Distinct black mark on each adipose crest posterior to black bar on caudal fin base. Smaller adults (<45 mm SL) similar to large adults in colour, but with 3–4 wide pre-dorsal bars ( Fig. 5 B).

In life: Large adults (> 45 mm) with light-brown body. Barbels with light-brown pigmentation. Bars on body wide, brown. Interspaces narrower, light brown. Black bar at caudal base complete, with its posterior margin vaguely indented at bases of branched caudal-fin rays 3 and 14. Pectoral, pelvic and anal fins with light-yellow pigmentation on rays. Rays of caudal and dorsal fins yellow. Interradial membrane of dorsal fin with melanophores medially. Prominent black blotch on anterior base of dorsal-fin; yellow stripe along dorsal-fin base, disappearing in preserved specimens.

Habitat and distribution. Schistura madhavai is at present known only from its type locality, a small stream about 2 m wide, flowing through sparsely-inhabited tea plantations in Suriyakanda in the Walawe River basin, at an elevation of about 1000 m above sea level ( Figure 6 ). The substrate consists of pebbles and gravel. Schistura madhavai prefers the faster-flowing regions of the stream. It shares its habitat also with the cyprinids Devario malabaricus (Jerdon) , Puntius titteya (Deraniyagala) , Pethia nigrofasciata (Günther) , Rasbora dandia (Valenciennes) , Rasboroides rohani (Batuwita, Silva & Edirisinghe) , and the osphronemid Belontia signata (Günther) . The guppy ( Poecilia reticulata Peters ; Poecillidae ), an exotic species, was also recorded from this locality. I sampled this habitat twice: once during a rainy period in November 2015 and again during a dry period in July 2016. I observed about seven adults in a stretch of ~ 10 m along the sampled length of the stream on the first occasion, and about five adults along the same stretch on my second visit. The stream-flow was very low during the latter visit and the water contained an algal bloom. The stream originates about 1 km upstream of the type locality, in a secondary-forest habitat. It joins an adjacent stream about 80 m downstream of the type locality. It was not possible to sample the adjacent streams and it could well be S. madhavai is found in these as well.

Molecular results. The neighbour-joining tree and the uncorrected pairwise distances for the two Sri Lankan species of Schistura are shown in Figure 7 and Table 3, respectively. Schistura madhavai and S. notostigma form a well-supported clade (bootstrap=91) that is sister to the Indian species. The interspecific uncorrected pairwise distance between S. madhavai and S. notostigma is 3.0–3.8%, while that between seven individuals of S. notostigma from two non-contiguous basins ( Table 1), was only 0.0–1.3%, lending support to the distinct specific identity of S. madhavai .

Etymology. The species name is a patronym honouring the evolutionary biologist Madhava Meegaskumbura, professor of Molecular Biology at University of Peradeniya. Formed as a noun in the genitive case.

Figures

FIGURE 1. Schistura madhavai, color in life (DZ 3418 C, 51.2 mm SL), Sri Lanka, Walawe River basin, Suriyakanda.

FIGURE 2. A, Lateral; B, dorsal; and C, ventral views of the holotype of Schistura madhavai (2017.02.01. NH), 49.7 mm SL.

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 5. Color pattern variation in Schistura madhavai: A, arrow indicating incomplete interspaces between post-dorsal bars (2017.03.01. NH, 55.3 mm SL); B, semi-adult with pre-dorsal bars (DZ 3458 D, 34.5 mm SL).

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 7. Neighbor-joining (NJ) tree for the 16 S rRNA gene fragment for selected species of Schistura using the K 2 P model (see Table 1 for list of material). The numbers on nodes represent the bootstrap values of the NJ tree. Nemacheilus corica is used as the outgroup. The scale bar represents 0.005 substitutions / changes.