Nemacheilus stigmofasciatus, a new species of nemacheiline loach (Cypriniformes: Balitoridae) from the Western Ghats, India

A new nemacheiline loach is described from the Seethanathi river of the Western Ghats, Karnataka. The new species differs from others of the genus in having an incomplete lateral line extending up to the end of the pelvic fin, shorter snout (35.9 -39.4% of HL) and bigger eyes (28.1-31.3% of HL). Notable colour variation is present in the bands on the back (11-13) and blotches (6-8) evenly spaced along the lateral line.


INTRODUCTION
The rich biodiversity and pristine habitats of many of the westward-flowing rivers of peninsular India have attracted many researchers for the exploration of new taxa.The area is especially significant for icthyologists as is evident from the discovery of two new nemacheiline loaches, Schistura shravathiensis and Schistura nagodiensis (Sreekantha et al. 2006) from the Shravathi river.The discovery is significant as these species have been collected from two streams of the same river basin.Also recently, the research team from Zoological Survey of India, Western Regional Station, Kozhikode, reported the collection of a new sisorid fish species from a stream inside Kudremukh National Park (to be published).
During our recent fish habitat survey in the main stream of the Seethanathi river in Karnataka, a few nemacheilines were collected having features distinct from known species; herein we describe a new species.The subfamily Nemacheilinae is readily distinguished from Balitorinae in having paired fins not inserted horizontally and with rounded abdomen.This genus has more than 450 species with distribution in southern China, South and southeast Asia, Baluchistan, western Iran and northeastern Africa (Kottelat et al. 1993).Fish of the genus Nemacheilus are characterized by a rather short dorsal fin (7 or 8 branched rays), a longitudinal stripe, which may be of lateral black band or black spots coalescing to form a band extending to caudal fin or distinct moniliform spots along the lateral line in the middle of body, large eyes, and a dark spot on the middle of the caudal base (Banarescue & Nalbant 1995).The genus Nemacheilus represents three valid species, namely Nemacheilus corica from northern India, and N. anguilla and N. monilis from southern India (Arunachalam & Muralidharan 2007).Nemacheilus anguilla Annandale was described from Medha river in Maharastra state and Nemacheilus monilis (Hora 1921) was described from Bhavani river near Mettupalayam, which is endemic to the streams of Nilgiri Hills.Nemacheilus poonaensis (Menon 1950) described from Moola-Mootha river of Krishna drainage is placed in synonymy with Nemacheilus anguilla (Menon 1987).Also Menon (1987) considers N. corica as belonging to Schistura, another related genus, whereas Banarescue & Nalbant (1995) include it under the genus Nemacheilus, which has also been followed by Jayaram (1999).

Diagnosis
Nemacheilus stigmofasciatus sp.nov. is distinguished from the other two peninsular Indian species N. anguilla and N. monilis by its colouration and a set of morphometric characters.The new species differs in having a lateral line that extends to the pelvic fin base below (vs.reaching up to anal fin in N. anguilla and complete in N. monilis), shorter snout length (35.939.4% HL vs 46.8% HL in N. anguilla and 40.548.1% HL in N. monilis), bigger eye (28.131.3%HL vs 23.0%HL in N. anguilla and 15.9-19.9% HL in N. monilis), caudal peduncle shorter than N. anguilla (12.413.1% SL vs 15.5% SL) and shallower than N. monilis (9.510.2%SL vs 12.014.5%SL).Vent to anal distance is reduced compared to N. anguilla (29.734.5% vs 40.6% Pelvic to anal distance) and greater than N. monilis (29.734.5% vs 16.925.9%Pelvic to anal distance).Notable colour variations are the lesser number of bands on dorsal (back) 1113 (vs 19-20 in N. anguilla and N. monilis), 68 blotches evenly spaced along the lateral line (vs.band formed of coalescing blotches extending to caudal base in N. anguilla and moniliform band in N. monilis).

Description
The general body shape and appearance are shown in Fig. 1.Morphometric data of the holotype and paratypes are given in Table 1.Body sub-cylindrical, dorsal profile slightly arched, dorsal region raises gradually from tip of snout to dorsal fin origin, followed by a gentle sloping for some extent and then evenly proceeds to caudal base.Ventral profile fairly convex.Depth of body (12.113.5 % in SL), head of moderate size and its length 23.524.8 % in SL.Snout short, blunt anteriorly, shorter than postorbital distance and its length 8.49.7 % in SL and 35.939.4 % in HL.Eyes large, placed dorsally in the mid of head length and not visible from ventral view.Nostrils close to each other with short flap, tubular but not extended as barbels.Mouth semicircular, lips moderately fleshy, deeply furrowed, upper lip with a pair of barbel like process at the arch, interrupted with a median incision, lower lip with small lobes and a median notch similar as in N. anguilla (Image 2).Dentiform process moderately developed.Barbels long and simple, two pairs rostral and one pair maxillary.Outer rostral pair, longest among barbels, extends almost to the anterior margin of eye.Maxillary barbels reaching to middle of eye.Entire body surface with uniformly small imbricate scales, except on the ventral side.Dorsal fin, slightly less than length of head, with four simple and eight branched rays, its origin well in advance to the perpendicular of pelvic fin origin, slightly ahead of midway between tip of snout and caudal base.
Pectoral fins with one simple and 1213 branched rays, extending to half way beyond the distance to pelvic origin.Pelvic fins with one simple and seven branched rays.Unculiferous pads on ventral surface of both paired fins, distinct in anterior most rays.Anal fin with three simple and five branched rays, its origin very far posterior, however, when compressed not reaching caudal fin base.Vent nearer to anal fin than to pelvic fin origin, which is overlapped by distal end of pelvic fin.Caudal fin deeply forked with well-developed upper and lower lobes, of equal length with 19 rays.Procurrent rays, beyond the caudal principal ray, 10 in upper lobe and seven in the lower lobe.Caudal peduncle short, its length 12.413.1 in percent of SL and its depth 75.076.8percent in its own length.

Colour
Head and body pale yellow with little greenish tinge.Head with numerous brownish patches distinct in inter-orbital and inter-nasal region.Dorsal region with 1113 dark brown vertical bands of varied thickness mostly as wide as interspaces (Image 1).Bands usually 3-4 in the predorsal region between occiput and dorsal region, four in the dorsal fin region (origin to distal end of the fin) and 4-5 in the post-dorsal region beyond the dorsal fin extension up to caudal base.Bands darker in the back, except for the two anterior most bands on lateral side, probably branched extensions of dorsal bands, first one as an elongated dot over upper angle of operculum and the second one as curved band from little above lateral line to half way along the anterior branched rays of pectoral fin diminishing afterwards.Rest others fade as they descend downward as incomplete bands, distinct upto lateral line beyond which they are less clear.Body with 68 longitudinally elongated dark brown blotches along the lateral line distributed in array upto caudal base, which end with the black spot a characteristic feature of genus Nemacheilus.The blotches along the lateral line are found to overlap or placed in between the forked bands.Dorsal fin has three black bands and caudal fin with melanin pigmentation as transverse rays in the median region.The sexual dimorphism as such is not exhibited, neither sub orbital flaps nor any form of colour indications have been noted.

Etymology
The specific name stigmofasciatus is a combination of the Greek words stigmo for blotch and fasciatus for band, due to the regularly sized blotches alternating with bands.

Distribution and habitat ecology
N. stigmofasciatus is represented only in the Seethanathi river at Thuttinjet.The Seethanathi is a small west-flowing river in Karnataka with many cascades and waterfalls in the upstream portion.The elevation of the stream at the type locality is 199m above sea level.The habitat in the study area is dominated by the presence of pebbles and boulders, gravels are lesser, sand constitutes about 5% of the total substrate.Riparian cover is about 20% and gradient is 3% and the banks are highly stable, left bank with thick vegetation while right bank is sparsely vegetated.Feeding was not observed in the field and gut contents were not examined due to the lesser number of specimens collected.

Comparison of species
Of the two valid species N. anguilla and N. monilis from peninsular India, the new species has more features in common with N. anguilla.The new species resembles other congeners with regards to prominent characters of the genus: blotches  along mid-lateral line, bands on the dorsal region, long barbels and occurrence of a dark spot on the median lobe of the caudal fin.N. monilis differs from the new species in having a bigger body, smaller eyes, a lateral line that reaches to the caudal base, prominent moniliform black spots, and also in having a mouth with upper lip poorly furrowed (Image 2).N. anguilla shows a closer resemblance, but the new species differs in several features: a lateral line that extends up to the pelvic fin, shorter snout, bigger eye diameter, shorter caudal peduncle, and pelvic fin extending beyond vent.Variation is also found in body colouration, with 67 roundish blotches along the mid lateral line along with a peculiar pattern of 1014 vertical bands varying in number and extension along the back to the lateral line.Both N. anguilla and N. stigmofasciatus sp.nov.have a pair of barbel-like processes interrupted with a median incision in their upper lip.However, the shape of the mouth opening differs a little, the tip of mouth is sharp in the form of inverted V shape in N. anguilla whereas it is curved and bell-shaped in N. stigmofasciatus sp.nov.Also the inner rostral barbels are not as short (Image 2) and the barbels are not as thick and fleshy as compared to those found in N. anguilla.